bluuebunny/crossref_metadata_2025 huggingface dataset:
Structure and metabolism of rat liver heparan sulphate
Authors: Oldberg Åke , Höök Magnus , Öbrink Björn , Pertoft Håkan , Rubin Kristofer
Published: August 2015

Rat liver cells grown in primary cultures in the presence of [35S]sulphate synthesize a labelled heparan sulphate-like glycosaminoglycan. The characterization of the polysaccharide as heparan sulphate is based on its resistance to digestion with chondroitinase ABC or hyaluronidase and its susceptibility to HNO2 treatment. The sulphate groups (including sulphamino and ester sulphate groups) are distributed along the polymer in the characteristic block fashion. In 3H-labelled heparan sulphate, isolated after incubation of the cells with [3H]galactose, 40% of the radioactive uronic acid units are l-iduronic acid, the remainder being d-glucuronic acid. The location of heparan sulphate at the rat liver cell surface is demonstrated; part of the labelled polysaccharide can be removed from the cells by mild treatment with trypsin or heparitinase. Further, a purified plasma-membrane fraction isolated from rats previously injected with [35S]sulphate contains radioactively labelled heparan sulphate. A proteoglycan macromolecule composed of heparan sulphate chains attached to a protein core can be solubilized from the membrane fraction by extraction with 6m-guanidinium chloride. The proteoglycan structure is degraded by treatment with papain, Pronase or alkali. The production of heparan [35S]sulphate by rat liver cells incubated in the presence of [35S]sulphate was followed. Initially the amount of labelled polysaccharide increased with increasing incubation time. However, after 10h of incubation a steady state was reached where biosynthetic and degradative processes were in balance.
Adenosine as a constituent of the brain and of isolated cerebral tissues, and its relationship to the generation of adenosine 3′:5′-cyclic monophosphate
Authors: Newman Michael , McIlwain Henry
Published: August 2015

1. Adenosine was determined in rapidly frozen rat and guinea-pig brain and in guinea-pig cerebral tissues after incubation in vitro. Adenosine concentrations were approx. 2nmol/g wet wt. in frozen tissue, diminished at room temperature, and returned to 2nmol/g on incubation in oxygenated glucose/salines. 2. Superfusion with noradrenaline then increased the tissue's adenosine concentration 2.5-fold, and hypoxia caused an 8-fold increase. 3. Electrical stimulation alone or in the presence of noradrenaline or histamine increased the tissue's adenosine and cyclic AMP, but adenosine concentrations reached their peak later and were maintained for longer than those of cyclic AMP. 4. Superfusion with l-glutamate with and without electrical excitation raised adenosine concentrations to 15–34nmol/g. The increases in cyclic AMP on electrical stimulation, superfusion with glutamate or a combination of these treatments were diminished by addition of adenosine deaminase or theophylline. 5. It is concluded that adenosine can be produced endogenously in cerebral systems, in sufficient concentrations to accelerate an adenosine-activated adenylate cyclase, and by this route can contribute to the cerebral actions of electrical stimulation and of the neurohumoral agents. In certain instances cyclic AMP as substrate contributes to an increase in adenosine.
The mechanism of inhibition by acidosis of gluconeogenesis from lactate in rat liver
Authors: Iles R A , Cohen R D , Rist A H , Baron P G
Published: August 2015

1. Gluconeogenesis from lactate or pyruvate was studied in perfused livers from starved rats at perfusate pH7.4 or under conditions simulating uncompensated metabolic acidosis (perfusate pH6.7-6.8). 2. In ‘acidotic’ perfusions gluconeogenesis and uptake of lactate or pyruvate were decreased. 3. Measurement of hepatic intermediate metabolites suggested that the effect of acidosis was exerted at a stage preceding phosphoenolpyruvate. 4. Total intracellular oxaloacetate concentration was significantly decreased in the acidotic livers perfused with lactate. 5. It is suggested that decreased gluconeogenesis in acidosis is due to substrate limitation of phosphoenolypyruvate carboxykinase. 6. The possible reasons for the fall in oxaloacetate concentration in acidotic livers are discussed; two of the more likely mechanisms are inhibition of the pyruvate carboxylase system and a change in the [malate]/[oxaloacetate] ratio due to the fall in intracellular pH.
The transport and metabolism of glutamine by kidney-cortex mitochondria from normal and acidotic rats
Authors: Brosnan J T , Hall B
Published: August 2015

1. The oxidation of glutamine by kidney-cortex mitochondria from normal and acidotic rats was not inhibited by avenaciolide, which did inhibit glutamate uptake and oxidation. The oxidation of glutamine by these mitochondria was always greater than that of glutamate. Direct measurements of the metabolism of [1-14C]glutamine in the presence of glutamate, and of [1-14C]glutamate in the presence of glutamine, demonstrated that the uptake and metabolism of external glutamate is insufficient to account for the observed rate of glutamine uptake and metabolism. Thus the postulated glutamine/glutamate antiport does not play a quantitatively important role in the metabolism of glutamine by renal mitochondria. 2. Rapid swelling of these mitochondria was observed in iso-osmotic solutions of L-glutamine and L-glutamyl-gamma-monohydroxamate but not in D-glutamine or L-isoglutamine (1-amido-2-aminoglutaric acid). Thus a relatively specific glutamine uniport exists in these mitochondria. 3. The utilization of glutamine was increased about 3-fold in mitochondria from chronically acidotic rats. Thus mitochondrial adaptations play an important part in the renal response to metabolic acidosis.
The effects of starvation and experimental diabetes on phosphoenol-pyruvate carboxykinase in the guinea pig
Authors: Elliott K R F , Pogson C I
Published: August 2015

1. Approx. 85% of liver phosphoenolpyruvate carboxykinase is associated with the mitochondrial fraction in the fed guinea pig. Enzyme activity is unchanged in diabetes, but doubles during starvation. In contrast with earlier reports, both cytoplasmic and mitochondrial activities were found to be increased. 2. In kidney cortex, total enzyme activity is increased in both starved and diabetic animals. These changes are associated with increases in the cytoplasmic activity alone. 3. In diabetic animals the mean blood-glucose concentration was 23.1 mM. Other blood metabolites were lower than those in the rat, and the animals did not show significant ketosis. 4. Changes in the rates of gluconeogenesis from lactate and propionate paralleled those in phosphoenolpyruvate carboxykinase activity.
Hypoketonaemic effect of L-alamine. Specific decrease in blood concentrations of 3-hydroxybutyrate in the rat
Authors: Ozand P T , Reed W D , Girard J , Hawkins R L , Collins R M , Tildon J T , Cornblath M
Published: August 2015

1. The injection of L-alanine (50-100 mg/kg) into 35-day-old rats that had been starveed for 48 h increased blood L-alanine concentration to values observed in fed animals and lowered the blood concentration of 3-hydroxybutyrate within 2 min. 2. This hypoketon aemic action of L-alanine was specific for 3-hydroxybutyrate, since the acetoacetate concentrations did not change significantly. 3. The decrease in 3-hydroxybutyrate elicited by L-alanine was not related to changes in the blood concentrations of insulin, glucagon, growth hormone, glucose, unesterified fatty acids, lactate or pyruvate. 4. The injection of L-alanine resulted in a decrease in total ketones that was apparently unrelated to their increased peripheral utilization. These results are interpreted as an anti-ketogenic action of L-alanine. 5. The data suggest that L-alamine lowers ketone-body formation in starved rats, possibly via an alteration in hepatic redox equilibrium.
Chitin biosynthesis in protoplasts and subcellular fractions of Aspergillus fumigatus
Authors: Archer D B
Published: August 2015

The biosynthesis of chitin has been obtained in broken mycelia and protoplasts of the fungus Aspergillus fumigatus. The specific activity of chitin synthase (EC 2.4.1.16) in a membrane preparation from protoplasts derived from the hyphal tips of A. fumigatus was 26.8-fold greater than that of the chitin synthase in broken mycelia, indicating that the active chitin synthase is located primarily in a membrane-bound site at the hyphal tip. Polyoxin D was a potent competitive inhibitor of the enzyme, having Ki 5.2 +/- 0.8 micron with respect to the natural substrate UDP-N-acetyl-D-glucosamine, which has Km 1.58 mM.
Interaction of the anti-oestrogen, nafoxidine hydrochloride, with the soluble nuclear oestradiol-binding protein in chick liver
Authors: Lazier C B , Alford W S
Published: August 2015

Nafoxidine hydrochloride (Upjohn, 11100A)injected with oestradiol into immature chicks inhibits the hormone-induced increase in [3H]oestradiol-binding activity in salt extracts of liver nuclei as well as the subsequent production by liver of egg-yolk phosphoprotein. Substantial inhibition of both oestradiol-induced responses is seen when nafoxidine is given in a dose approximately equimolar with that of oestradiol. In vitro nafoxidine competitively inhibits binding of [3H]oestradiol in nuclear extracts. The Ki for the inhibition is 43 nM, which indicates an affinity of nafoxidine for the binding protein about 4% of that of oestradiol. The inhibitory action of nafoxidine in vivo thus is more potent than the relative binding affinity determined in vitro might indicate. One possible explanation is that the primary site of nafoxidine action is at a point proximal to nuclear receptor interaction. Nafoxidine injected alone into the chick does not induce phosphoprotein synthesis, but it does increase [3H]oestradiol-binding activity in extracts of liver nuclei to a limited extent. No differences in the properties of the oestradiol-binding activity in extracts from nafoxidine-treated chicks or from oestradiol-treated chicks were detected. Chick liver cytosol does not contain detectable high-affinity oestradiol-binding activity. A low-affinity oestradiol-binding component with a sedimentation coefficient of 3.5S was found, but it was unaffected by treatment of chicks with earlier nafoxidine or oestradiol. The results suggest a difference in the mechanism of oestradiol action in the chick liver and in the widely studied rat uterus, on which the usual model for oestradiol action is largely based.
Adenosine 3′:5′-cyclic monophosphate in higher plants: Isolation and characterization of adenosine 3′:5′-cyclic monophosphate from Kalanchoe and Agave
Authors: Ashton A R , Polya G M
Published: August 2015

1.3′:5′-Cyclic AMP was extensively purified from Kalanchoe daigremontiana and Agave americana by neutral alumina and anion- and cation-exchange column chromatography. Inclusion of 3′:5′-cyclic [8-3H]AMP from the point of tissue extraction permitted calculation of yields. The purification procedure removed contaminating material that was shown to interfere with the 3′:5′-cyclic AMP estimation and characterization procedures. 2. The partially purified 3′:5′-cyclic AMP was quantified by means of a radiochemical saturation assay using an ox heart 3′:5′-cyclic AMP-binding protein and by an assay involving activation of a mammalian protein kinase. 3. The plant 3′:5′-cyclic AMP co-migrated with 3′:5′-cyclic [8-3H]AMP on cellulose chromatography, poly(ethyleneimine)-cellulose chromatography and silica-gel t.l.c. developed with several solvent systems. 4. The plant 3′:5′-cyclic AMP was degraded by ox heart 3′:5′-cyclic nucleotide phosphodiesterase at the same rates as authentic 3′:5′-cyclic AMP. 1-Methyl-3-isobutylxanthine (1 mM), a specific inhibitor of the 3′:5′-cyclic nucleotide phosphodieterase, completely inhibited such degradation. 5. The concentrations of 3′:5′-cyclic AMP satisfying the above criteria in Kalanchoe and Agave were 2-6 and 1 pmol/g fresh wt. respectively. Possible bacterial contribution to these analyses was estimated to be less than 0.002pmol/g fresh wt. Evidence for the occurrence of 3′:5′-cyclic AMP in plants is discussed.
Purification and properties of human kidney-cortex hexosaminidases A and B
Authors: Wiktorowicz J E , Awasthi Y C , Kurosky A , Srivastava S K
Published: August 2015

Hexosaminidases (EC 3.2.1.30) A and B from human kidney cortex were purified to homogeneity by using concanavalin A affinity chromatography, ion-exchange chromatography and gel filtration. The yield of homogeneous isoenzymes improved approx. 20-fold, giving preparations of hexosaminidases A and B with specific activities of about 200 and 325 units/mg of protein respectively. The kinetic and structural properties of kidney hexosaminidase isoenzymes were studied and compared with the hexosaminidase isoenzymes from human placenta. The amino acid composition of hexosaminidase A was significantly different from that of hexosaminidase B. In the event of success in developing enzyme-replacement therapy for Tay-Sachs and Sandhoff's diseases, this modified procedure can furnish larger amounts of homogeneous isoenzymes.
Subtilisin modification of monodeamidated ribonuclease-A
Authors: Manjula B. N. , Acharya A. Seetharama , Vithayathil Paul J.
Published: August 2015

Limited proteolysis of RNAase-Aa1 (monodeamidated ribonuclease-A) by subtilisin results in the formation of an active RNAase-S type of derivative, namely RNAase-Aa1S. RNAase-Aa1S was chromatographically distinct from RNAase-S, but exhibited very nearly the same enzymic activity, antigenic conformation and susceptibility to trypsin as did RNAase-S. Fractionation of RNAase-Aa1S by trichloroacetic acid yielded RNAase-Aa1S-protein and RNAase-Aa1S-peptide, both of which are inactive by themselves, but regenerate active RNAase-Aa1S′ when mixed together. RNAase-Aa1S-peptide was identical with RNAase-S-peptide, whereas the protein part was distinct from that of RNAase-S-protein. Titration of RNAase-Aa1S-protein with S-peptide exhibited slight but noticeably weaker binding of the peptide to the deamidated S-protein as compared with that of native protein. Unlike the subtilisin digestion of RNAase-A, which gives nearly 100% conversion into RNAase-S, the digestion of RNAase-Aa1 gives only a 50% conversion. The resistance of RNAase-Aa1 to further subtilisin modification after 50% conversion is apparently due to the interaction of RNAase-Aa1 with its subtilisin-modified product. RNAase-S was also found to undergo activity and structural changes in acidic solutions, similar to those of RNAase-A. The initial reaction product (RNAase-Sa1) isolated by chromatography was not homogeneous. Unlike the acid treatment of RNAase-A, which affected only the S-protein part, the acid treatment of RNAase-S affected both the S-protein and the S-peptide region of the molecule.
Effect of substrates and effectors on the reversible inactivation of pig spleen phosphofructokinase by adenosine triphosphate
Authors: Weidemann Maurice J. , Kolbuch-Braddon Marysia E. , Hickman Peter E.
Published: August 2015

1. To investigate the mechanism of the reversible inactivation of pig spleen phosphofructokinase by ATP, the effect of order of addition of reactants (substrates, effectors and enzyme solution) was studied by preincubating the enzyme before assay with various combinations of its substrates and effectors. 2. Preincubation of the enzyme with MgATP or ATP at pH7.0 before addition of fructose 6-phosphate caused a rapid and much greater inhibition of activity than that observed when the reaction (carried out at identical substrate concentrations) was initiated with enzyme. 3. The rapid inhibition caused by preincubation with ATP, together with the sigmoidal response to fructose 6-phosphate and activation by AMP, were all blocked by prior photo-oxidation of the enzyme with Methylene Blue, which selectively destroys the inhibitory binding site for ATP [Ahlfors & Mansour (1969) J. Biol. Chem.244, 1247–1251]. 4. Fructose 6-phosphate, but not Mg2+, protected phosphofructokinase from inhibition during preincubation with ATP in a manner that was sigmoidally dependent on the fructose 6-phosphate concentration. 5. Mg2+, by protecting the enzyme from the inhibitory effect of preincubation at low pH (7.0) and by preventing its activation during preincubation with fructose 6-phosphate, demonstrated both a weak activating effect in the absence of the other substrates and a stronger inhibitory effect in the presence of fructose 6-phosphate. 6. Positive effectors (K+, NH4+, AMP and aspartate) protected the enzyme from inhibition during preincubation with MgATP in proportion to their potency as activators, but citrate potentiated the ATP inhibition. Pi significantly slowed the inactivation process without itself acting as a positive effector. 7. The non-linear dependence of the initial rate of the unmodified enzyme on protein concentration (associated with increased positive homotropic co-operativity to fructose 6-phosphate) was intensified by preincubation with ATP and abolished by photo-oxidation. 8. The results are interpreted in terms of an association–dissociation model which postulates that protonation, at low pH, of a photo-oxidation-sensitive inhibitory site for ATP allows more rapid dissociation of an active tetramer to an inactive dimeric species.
The role of tubular reabsorption in the renal excretion of bile acids
Authors: Barnes S , Gollan J L , Billing B H
Published: August 2015

1. The renal excretion of bile acids was studied in an isolated rat kidney preparation perfused with a protein-free medium. 2. Tubular reabsorption exceeded 95% for both non-sulphated and sulphated bile acids at filtered loads of less than 30 nmol/min. 3. At low filtered loads the reabsorption of taurocholate and taurochenodeoxycholate was almost complete. Efficient reabsorption of taurochenodeoxycholate was maintained over a wider range of filtered loads than for taurocholate. These observations suggest that active transport may occur. 4. At high filtered loads saturation of reabsorption of taurocholate and taurochenodeoxycholate did not occur, which indicates that passive diffusion is involved in reabsorption. 5. Active proximal-tubular secretion of bile acids was not demonstrated in competition experiments with p-aminohippurate. 6. The fractional reabsorption of taurocholate, chenodeoxycholate 3,7-disulphate and chenodeoxycholate 7-monosulphate was decreased by the addition of taurochenodeoxycholate to the perfusate, so that their renal excretion was enhanced. This interaction between the bile acids for reabsorption may explain the different composition of bile acids in urine compared with that in plasma in cholestasis in man. 7. Conjugated bilirubin decreased the fractional reabsorption of both taurocholate and taurochenodeoxycholate at low filtered loads (less than 30 nmol/min) but not at high filtered loads (400 nmol/min).
Polyamines and their biosynthetic enzymes in Ehrlich ascites-carcinoma cells. Modification of tumour polyamine pattern by diamines
Authors: Kallio A , Pösö H , Guha S K , Jänne J
Published: August 2015

1. Ehrlich ascites-carcinoma cells contained relatively high concentrations of spermidine and spermine, but the putrescine content of the washed cells was less than 10% of that of higher polyamines. 2. Ascites-tumour cells likewise exhibited high activities of L-ornithine decarboxylase (EC 4.1.1.17), S-adenosyl-L-methionine decarboxylase (EC 4.1.1.50), spermidine synthase (EC 2.5.1.16) and spermine synthase. 3. During the first days after the inoculation, the polyamine pattern of the ascites cells was characterized by a high molar ratio of spermidine to spermine, which markedly decreased on aging of the cells. 4. Various diamines injected into mice bearing ascites cells rapidly and powerfully decreased ornithine decarboxylase activity in the carcinoma cells, apparently through a mechanism that was not a direct inhibition of the enzyme in vitro. Cadaverine (1,5-diaminopentane) and 1,6-diaminohexane were the most potent inhibitors of ornithine decarboxylase among the amines tested. 5. Chronic treatment of the mice with diamines resulted in a virtually complete disappearance of ornithine decarboxylase activity, and after 24h a significant decline in spermidine accumulation. 6. Cadaverine appeared to be an especially suitable compound for use as an inhibitor of the synthesis of higher polyamines, at least in Ehrlich ascites cells, since this diamine also acted as a competitive inhibitor for putrescine in the spermidine synthase reaction without being incorporated into the higher polyamines.
Specific protein synthesis in isolated epithelium of guinea-pig seminal vesicle. Effects of castration and androgen replacement
Authors: Veneziale Carlo M. , Burns John M. , Lewis Jon C. , Büchi Kaspar A.
Published: August 2015

Four intrinsic soluble secretory proteins are synthesized in vitro by isolated seminal-vesicle mucosa from sexually mature guinea pigs. Newly synthesized specific proteins labelled with [14C]glycine and [14C]lysine were precipitated by using double-antibody immunoprecipitation techniques and their radioactivity was assessed. Rates of synthesis were determined on each of 5 days after castration. By 5 days after castration the wet weight of the epithelium decreased to 42% of intact control values; the absolute amount of specific protein synthesized in vitro after 60min incubation decreased to 28% and the 27500g cytoplasmic protein content decreased to 31%. Thus androgen deprivation leads to a decrease in general protein synthesis in vivo, as well as to a decrease in specific protein synthesis in vitro. Specific protein synthesis comprised 76% of the total protein formed in isolated tissue from animals 5 days after castration as compared with 99–100% in tissue from intact animals. At 72h after an injection of testosterone or dihydrotestosterone, seminal-vesicle epithelium wet weight, cytoplasmic protein content and capability for synthesizing specific proteins in vitro were restored to approx. 70% of normal values. At 72h after onset of therapy with 3α-androstanediol, both epithelium wet weight and cytoplasmic protein content had increased significantly, but without a corresponding increase in the capability of the isolated tissue to synthesize specific proteins. The soluble labelled proteins synthesized in vitro by isolated epithelium from intact animals during 60 or 120min incubation were essentially entirely immunoprecipitable, i.e. specific. In contrast, approx. 29% of all soluble protein newly synthesized by isolated epithelium from animals 5 days after castration was acid-precipitable, but not immunoprecipitable, i.e. ‘non-specific’. The injection of testosterone into castrated animals inhibited the synthesis of the non-specific fraction by isolated tissue. The effects of castration on the ultrastructure of guinea-pig seminal-vesicle epithelium are also presented.
Bacterial catabolism of threonine. Threonine degradation initiated by l-threonine acetaldehyde-lyase (aldolase) in species of Pseudomonas
Authors: Bell Stephen C. , Turner John M.
Published: August 2015

1. The route of l-threonine degradation was studied in four strains of the genus Pseudomonas able to grow on the amino acid and selected because of their high l-threonine aldolase activity. Growth and manometric results were consistent with the cleavage of l-threonine to acetaldehyde+glycine and their metabolism via acetate and serine respectively. 2. l-Threonine aldolases in these bacteria exhibited pH optima in the range 8.0–8.7 and Km values for the substrate of 5–10mm. Extracts exhibited comparable allo-l-threonine aldolase activities, Km values for this substrate being 14.5–38.5mm depending on the bacterium. Both activities were essentially constitutive. Similar activity ratios in extracts, independent of growth conditions, suggested a single enzyme. The isolate Pseudomonas D2 (N.C.I.B. 11097) represents the best source of the enzyme known. 3. Extracts of all the l-threonine-grown pseudomonads also possessed a CoA-independent aldehyde dehydrogenase, the synthesis of which was induced, and a reversible alcohol dehydrogenase. The high acetaldehyde reductase activity of most extracts possibly resulted in the underestimation of acetaldehyde dehydrogenase. 4. l-Serine dehydratase formation was induced by growth on l-threonine or acetate+glycine. Constitutively synthesized l-serine hydroxymethyltransferase was detected in extracts of Pseudomonas strains D2 and F10. The enzyme could not be detected in strains A1 and N3, probably because of a highly active ‘formaldehyde-utilizing’ system. 5. Ion-exchange and molecular exclusion chromatography supported other evidence that l-threonine aldolase and allo-l-threonine aldolase activities were catalysed by the same enzyme but that l-serine hydroxymethyltransferase was distinct and different. These results contrast with the specificities of some analogous enzymes of mammalian origin.
Induction of human choriogonadotropin in HeLa-cell cultures by aliphatic monocarboxylates and inhibitors of deoxyribonucleic acid synthesis
Authors: Ghosh Nimai K. , Rukenstein Adriana , Cox Rody P.
Published: August 2015

The ectopic production of the glycopeptide hormone human placental choriogonadotropin by HeLa65 cells was measured by radioimmunoassay with antiserum against the β-subunit of choriogonadotropin and with the125I-labelled β-subunit as a tracer antigen. Choriogonadotropin synthesis was markedly (500-fold) stimulated by sodium butyrate. Kinetic studies and the use of an inhibitor of protein synthesis, cycloheximide, indicated that protein synthesis was required for this induction. Investigation of the efficiency of 22 aliphatic short-chain fatty acids and derivatives in causing increased choriogonadotropin synthesis by HeLa cells showed stringent structural requirements. Induction of choriogonadotropin synthesis in HeLa cells was not restricted to butyrate. Other aliphatic acids (propionate, isobutyrate, valerate and hexanoate) were also capable of inducing choriogonadotropin synthesis at 10–50% of the efficiency of butyrate. Hydroxy derivatives of monocarboxylate inducers, related mono- and di-carboxylic acids, alcohols, amines, ketones, esters and sulphoxide were ineffective in increasing choriogonadotropin production by HeLa cells. A saturated C4 straight-chain acid without substituent hydroxyl groups but with a methyl group at one end and a carboxyl moiety at the other appeared to be most efficient in activating choriogonadotropin production. A second clonal line of HeLa cells, HeLa71, showed a higher constitutive synthesis of choriogonadotropin than HeLa65 cells, which was also markedly increased by butyrate. Butyrate and other aliphatic monocarboxylate inducers of choriogonadotropin synthesis inhibited HeLa-cell growth and DNA synthesis. This inhibition of DNA replication may be related to the mechanism of choriogonadotropin synthesis, since two well-characterized anti-neoplastic inhibitors of DNA synthesis, hydroxyurea and 1-β-d-arabinofuranosylcytosine, also stimulated a 300-fold increase in choriogonadotropin synthesis in HeLa cells and were synergistic with butyrate in promoting choriogonadotropin synthesis. Thus activation in tumour cells of genes normally expressed by foetal tissue and the consequent ectopic synthesis of polypeptide hormones may require neither cell division nor DNA synthesis.
The effects of altered membrane sterol composition on oxidative phosphorylation in a haem mutant of Saccharomyces cerevisiae
Authors: Astin Anne M. , Haslam J. M.
Published: August 2015

1. The sterol, unsaturated fatty acid and cytochrome contents of cells of a δ-aminolaevulinate synthase mutant of Saccharomyces cerevisiae are manipulated by growing the organism in media containing defined supplements of δ-aminolaevulinate and other porphyrin intermediates. 2. If unsaturated fatty acids are added to the growth medium as Tween 80, sterol content and respiratory cytochromes alone are manipulated. 3. In the presence of δ-aminolaevulinate (10–50mg/1) cells exhibit moderate to high respiratory activity, but growth yields are low, indicating a loss of oxidative phosphorylation. This is associated with the depletion of membrane lipids, either unsaturated fatty acids and sterols together or sterols alone. 4. Sterol depletion leads to the loss of coupled mitochondrial oxidative phosphorylation in vitro. 5. The lesion in oxidative phosphorylation is associated with an increase in the passive permeability of sterol-depleted mitochondria to protons. 6. Arrhenius plots of mitochondrial permeability to protons indicate that the activation energy for proton entry increases as the sterol content of the membranes decreases. 7. Studies on a cytoplasmic petite mutant isolated from strain ole-3, which lacks a functional membrane-bound protein-translocating adenosine triphosphatase, indicate that proton permeability of the petite mitochondria varies as a function of sterol composition in the same way as that of ole-3 grande mitochondria. This indicates that sterols alone are probably directly responsible for the increased proton entry, owing to a reorganization of the lipid in the membrane. 8. Supplemented ole-3 cells with a normal lipid composition and normal or higher than normal respiratory activities have a growth efficiency only 65% of that of the wild-type, indicating that a further lesion in energy metabolism may be present.
S-Adenosylmethionine metabolism and its relation to polyamine synthesis in rat liver. Effect of nutritional state, adrenal function, some drugs and partial hepatectomy
Authors: Eloranta Terho O. , Raina Aarne M.
Published: August 2015

S-Adenosylmethionine metabolism and its relation to the synthesis and accumulation of polyamines was studied in rat liver under various nutritional conditions, in adrenalectomized or partially hepatectomized animals and after treatment with cortisol, thioacetamide or methylglyoxal bis(guanylhydrazone) {1,1′-[(methylethanediylidine)dinitrilo]diguanidine}. Starvation for 2 days only slightly affected S-adenosylmethionine metabolism. The ratio of spermidine/spermine decreased markedly, but the concentration of total polyamines did not change significantly. The activity of S-adenosylmethionine decarboxylase initially decreased and then increased during prolonged starvation. This increase was dependent on intact adrenals. Re-feeding of starved animals caused a rapid but transient stimulation of polyamine synthesis and also increased the concentrations of S-adenosylmethionine and S-adenosylhomocysteine. Similarly, cortisol treatment enhanced the synthesis of polyamines, S-adenosylmethionine and S-adenosylhomocysteine. Feeding with a methionine-deficient diet for 7–14 days profoundly increased the concentration of spermidine, whereas the concentrations of total polyamines and of S-adenosylmethionine showed no significant changes. The results show that nutritional state and adrenal function play a significant role in the regulation of hepatic metabolism of S-adenosylmethionine and polyamines. They further indicate that under a variety of physiological and experimental conditions the concentrations of S-adenosylmethionine and of total polyamines remain fairly constant and that changes in polyamine metabolism are not primarily connected with changes in the accumulation of S-adenosylmethionine or S-adenosylhomocysteine.
Modulation of the response of bovine adrenocortical adenylate cyclase to corticotropin
Authors: Glynn P , Cooper D M F , Schulster D
Published: August 2015

An assessment was made of some of the basic parameters responsible for the modulation of adenylate cyclase activity in a bovine adrenocortical plasma-membrane preparation. When determined at 0.1 mM-ATP, basal adenylate cyclase activity increased with increasing MgCl2 concentrations, whereas in the presence of corticotropin activity was essentially maximal at 10mM-MgCl2; high concentrations (25mM) of MgCl2 inhibited adenylate cyclase activity determined in the presence of both corticotropin and GTP. At all MgCl2 concentrations, corticotropin and GTP activated the enzyme in a synergistic fashion. The magnitude of the stimulation of basal activity produced by corticotropin was a function of Mg2+ concentration, whereas that produced by GTP appeared largely independent of Mg2+ concentration. Adenylate cyclase activity in the bovine adrenal membrane was half-maximally stimulated by corticotropin concentrations in the range 0.3—1.0 nM. The concentration of corticotropin evoking half-maximum response was not significantly affected by raising the free Mg2+ concentration from 0.4 to 4.9 mM, nor by the presence of GTP. In the presence of GTP, high concentrations (over 1 micrometer) of corticotropin inhibited adenylate cyclase activity, although no inhibition was apparent in the absence of guanine nucleotide.
Protein phosphorylation in normal and neoplastic development. Cyclic AMP-dependent protein kinase activity in urethane-induced pulmonary tumours
Authors: Malkinson A M , Gunderson T J , McSwigan C E
Published: August 2015

The cyclic AMP-dependent protein kinase specific activities of cytosol fractions from urethane-induced lung tumours and from normal mouse lung were determined. Both basal and cyclic AMP-stimulated activities in tumours were twofold higher than those of normal lung. Since neonatal and adult lung cytosols have identical kinase activities, the high activity in tumours appears to be a tumour-specific property.
A comparison of the effects of prednisolone and methylprednisolone on human lymphoblastoid cells
Authors: Waddell A W , Currie A R
Published: August 2015

Methylprednisolone is more effective than prednisolone in mediating long-term cytolysis and immediate inhibition of nucleoside uptake in human lymphoblastoid cells. This suggests that methylation of prednisolone makes it more potent by aiding interaction with a cellular target rather than increasing its stability.
Oxidative phosphorylation. Halide-dependent and halide-independent effects of triorganotin and trioganolead compounds on mitochondrial functions
Authors: Aldridge W N , Street B W , Skilleter D N
Published: August 2015

1. Each of five triorganotin and five triorganolead compounds was shown to perturb mithochondrial functions in three different ways. One is dependent and two are independent of Cl- in the medium. 2. Structure-activity relationships for the three interactions are described, and compounds suitable as tools for the separate study of each process are defined. 3. In a Cl- -containing medium trimethyltin, triethyltin, trimethyl-lead, triethyl-lead and tri-n-propyl-lead all produce the same maximum rate of ATP hydrolysis and O2 uptake; this rate is much less than that produced by uncoupling agents such as 2,4-dinitrophenol. 4. Increase in ATP hydrolysis and O2 uptake are measures on energy ultilization when triogranotin and triorganolead compounds bring about an exchange of external C1- for intramitochondrial OH- ions. Possible rate-limiting steps in this process are discussed. 5. In a C1- -containing medium ATP synthesis linked to the oxidation of beta-hydroxybutyrate or reduced cytochrone c is less inhibited by triethyltin or triethyl-lead than is ATP synthesis linked to the oxidation of succinate, pyruvate or L-glutamate. 6. The inhibition of ATP synthesis linked to the oxidation of both beta-hydroxybutyrate and reduced cytochrome c consists of two processes: one is a limited uncoupling and is C1- -dependent and the other is a C1- -independent inhibition of the energy-conservation system. 7. The different sensitivities to inhibition by triethyltin of mitochondrial functions involving the oxidation of beta-hydroxybutyrate and succinate are compared and discussed.
Control of glucose metabolism in isolated acini of the lactating mammary gland of the rat. The ability of glycerol to mimic some of the effects of insulin
Authors: Robinson A M , Williamson D H
Published: August 2015

Inhibition of glucose uptake by acetoacetate and relief of this inhibition by insulin found previously in slices of rat mammary gland [Williamson, McKeown & Ilic (1975) Biochem. J. 150. 145-152] was confirmed in acini, which represent a more homogeneous population of cells. Glycerol (1mM) behaved like insulin (50 minuits/ml) in its ability to relieve the inhibition of glucose (5 mM) utilization caused by acetoacetate (2 mM) in acini. Both glycerol and insulin reversed the increase in [citrate] and the decrease in [glycerol 3-phosphate] and the [lactate]/[pyruvate] ratio in the presence of acetoacetate. Lipogenesis from 3H2O, [3-14C] acetoacetate, [1-14C]- and [6-14C]-glucose was stimulated, whereas 14CO2 formation from [3-14C]acetoacetate was decreased. Neither insulin nor glycerol relieved the acetoacetate inhibition of glucose uptake when lipogenesis was inhibited by 5-(tetradecyloxy)-2-furoic acid. From measurements of [3-14C]acetoacetate incorporation into lipid in the various situations it is suggested that a cytosolic pathway for acetoacetate utilization may exist in rat mammary gland. In the absence of acetoacetate, glycerol inhibited glucose utilization by 60% and increased both [glycerol 3-phosphate] and the [lactate/[pyruvate] ratio. Possible ways in which glycerol may mimic the effects of insulin are discussed.
Tryptophan and the control of plasma glucose concentrations in the rat
Authors: Smith S A , Pogson C I
Published: August 2015

1. Injection of L-tryptophan (750 mg/kg body wt.) led to pronounced hypoglycaemia in fed and 48 h-starved rats. 2. The hypoglycaemic effect is blocked by pretreament with p-chlorophenylalanine, compound MK-486 [Carbidopa: L-alpha-(3,4-dihydroxybenzyl)-alpha-hydrazinopropionic acid monohydrate] or methysergide, and potentiated by pargyline. 3. 5-Hydroxy-L-tryptophan is more potent and induces a more rapid hypoglycaemia than does tryptophan. Other tryptophan metabolites were not associated with hypoglycaemia. 4. Adrenalectomy increases, and acute experimental diabetes strongly decreases, the sensitivity of rats to tryptophan induction of hypoglycaemia. Diabetic animals were also insensitive to 5-hydroxytryptophan. 5. Metabolite concentration changes in the livers from tryptophan-treated 48h-starved and diabetic animals were consistent with a rapid inhibition of gluconeogenesis. This did not correlate with the hypoglycaemic response. 6. Tryptophan treatment was associated with a significant increase in the plasma [beta-hydroxybutyrate]/[acetoacetate] ratio; there were no changes in the plasma concentrations of urea, triacyglycerol, non-esterified fatty acids and glycerol. 7. These observations suggest that the hypoglycaemic action of tryptophan is mediated through formation of intracellular 5-hydroxytryptamine, and is unrelated to the inhibition of gluconeogenesis. It is unlikely that this increased synthesis of 5-hydroxytryptamine involves directly either the adrenal glands or the central nervous system.
Effect of removal of calcium-activated adenosine triphosphatase from rat mast cells by treatment with sodium glycocholate
Authors: Cooper P H , Stanworth D R
Published: August 2015

Sodium glycocholate was shown to remove a Ca2+-activated adenosine triphosphatase from the external surface of the rat mast cell without causing lysis. Sensitized mast cells pretreated with sodium glycocholate showed a decrease in histamine-releasing capacity when triggered with antigen, Synacthen and ATP. Release induced by calcium ionophore A23187 was unaffected.
A species difference in nucleoside phosphorylase activity and inosine-stimulated insulin secretion in isolated islets of Langerhans
Authors: Campbell I L , Taylor K W
Published: August 2015

Inosine is a potent simulant of insulin release from rat but not from rabbit islets of Langerhans. Further investigation showed that nucleoside phosphorylase activity is exceptionally low in rabbit islets. The ability of inosine to promote insulin release seems to be related to islet nucleoside phosphorylase activity, which can display marked species differences.
Activation of immobilized acetyl-Coenzyme A carboxylase
Authors: Landman A D , Lampert J
Published: August 2015

Partially purified acetyl-CoA carboxylase was covalently bound to a Sepharose 4B matrix. Although aggregation was thus prevented, the enzymic activity was stimulated by citrate and isocitrate.
Purification and properties of a nuclear protein kinase associated with ribonucleic acid polymerase I
Authors: Hirsch J , Martelo O J
Published: August 2015

A cyclic AMP-dependent nuclear protein kinase was found to be closely associated with rat liver nucleolar RNA polymerase I throughout most of its purification. This protein kinase was purified to near homogeneity. It exhibits a number of unusual catalytic properties, including the inability to utilize Mn2+ when RNA polymerase is the substrate and the ability to phosphorylate both acidic and basic substrates. Phosphorylation of RNA polymerase I by this protein kinase results in the formation of phosphoester bonds characteristic of phosphoserine and phosphothreonine. Radioautography of polyacrylamide-gel electrophoretograms of the phosphorylated RNA polymerase I revealed that the 32P was located primarily on enzyme subunits SA1, SA3, SA5, and SA6 [nomenclature of Kedinger, Gissinger & Chambon (1974) Eur. J. Biochem, 44, 421-436].
Thermal denaturation of Micrococcus lysodeikticus adenosine triphosphatase. Influence of temperature on the circular dichroism, fluroescence and enzymic activity of the protein
Authors: Ayala J A , Nieto M
Published: August 2015

The soluble ATPase (adenosine triphosphatase) from Micrococcus lysodeikticus underwent a major unfolding transition when solutions of the enzyme at pH 7.5 were heated. The midpoint occurred at 46 degrees C when monitored by changes in enzymic activity and intrinsic fluorescence, and at 49 degrees C when monitored by circular dichroism. The products of thermal denaturation retained much secondary structure, and no evidence of subunit dissociation was detected after cooling at 20 degrees C. The thermal transition was irreversible, and thiol groups were not involved in the irreversibility. The presence of ATP, adenylyl imidodiphosphate, CaCl2 or higher concentrations of ATPase conferred stability against thermal denaturation, but did not prevent the irreversibility one denaturation had taken place. In the presence of guanidinium chloride, thermal denaturation occurred at lower temperatures. The midpoints of the transition were 45 degrees C in 0.25 M-, 38 degrees C in 0.5 M-and 30 degrees C in 0.75 M-denaturant. In the highest concentration of guanidinium chloride a similar unfolding transition induced by cooling was observed. Its midpoint was 9 degrees C, and the temperature of maximum stability of the protein was 20 degrees C. The discontinuities occurring the the Arrhenius plots of the activity of this enzyme had no counterpart in variations in the far-u.v. circular dichroism or intrinsic fluorescence of the protein at the same temperature.
A theoretical analysis of the use of zonal gel filtration in the detection and purification of protein-ligand complexes
Authors: Nimmo I A , Bauermeister A
Published: August 2015

A simple model of zonal gel filtration is analysed numerically to establish semiquantitatively how the capacity of a protein-ligand complex to survive gel filtration intact depends on several experimental variables and on the kinetic characteristics of the complex. The design of gel-filtration experiments aimed at detecting and partially purifying binding proteins is discussed.
Malate dehydrogenase of the cytosol. Preparation and reduced nicotinamide–adenine dinucleotide-binding studies
Authors: Lodola Alberto , Spragg S. Peter , Holbrook J. John
Published: August 2015

1. Two methods of preparing pig heart soluble malate dehydrogenase are described. A slow method yields an enzyme composed of three electrophoretically separable subforms. The more rapid method reproducibly gives a high yield of an enzyme that consists predominantly of the least acid subform. 2. The A1%1cm of the protein was redetermined as 15 at 280nm. By using this value the enzyme molecule was found to contain two independent and indistinguishable NADH-binding sites in titrations with NADH. 3. No evidence was found for the dissociation of the enzyme in the concentration range 0.02–7.2μm. 4. l-Malate (0.1m) tightened the binding of NADH to both pig and ox heart enzyme (2-fold), but, in contrast with the report by Mueggler, Dahlquist & Wolfe [(1975) Biochemistry14, 3490–3497], did not cause co-operative interactions between the binding sites. 5. Fructose 1,6-bisphosphate had no effect on the binding of NADH to the pig heart enzyme, but with the ox heart enzyme the NADH is slowly oxidized. This slow oxidation explains the ‘sigmoidal’ binding curves obtained when NADH was added to ox heart soluble malate dehydrogenase in the presence of fructose 1,6-bisphosphate [Cassman (1973) Biochem. Biophys. Res. Commun.53, 666–672] without the postulate of site–site interactions. 6. It is concluded that neither l-malate nor fructose 1,6-bisphosphate could in vivo modulate the activity of soluble malate dehydrogenase and alter the rates of transport of NADH between the cytosol and the mitochondrion. 7. Details of the preparation of soluble malate dehydrogenase have been deposited as Supplementary Publication SUP 50080 (8 pages) at the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies may be obtained under the terms given in Biochem. J. (1978) 169, 5.
Isolation and partial characterization of rabbit plasma α1-antitrypsin
Authors: Koj A , Hatton M W C , Wong K L , Regoeczi E
Published: August 2015

Alpha1-Antitrypsin was isolated from rabbit plasma by salting out with (NH4)2SO4 followed by ion-exchange chromatography either on DEAE-Sephadex or DEAE-cellulose (each at pH8.8 and 6.5), and affinity chromatography on Sepharose-Cibacron Blue and Sepharose-concanavalin A. The protein thus obtained was homogeneous during crossed immunoelectrophoresis by using an antiserum to whole rabbit plasma, but it migrated as two broad bands when electrophoresed in alkaline polyacrylamide gels. Under optimal loading conditions, two or three subcomponents could be distinguished in each band. The two major forms of rabbit alpha1-antitrypsin, designated components F and S, were separated by preparative polyacrylamide-gel electrophoresis, and some of their physico-chemical properties were established. Both forms reacted with trypsin at a molar ratio of 1:1. Their elution volumes from a Sephadex G-200 column were identical, corresponding to a mol.wt. of 58000; however, some heterogeneity was observed after sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. Isoelectric focusing in polyacrylamide gel in a pH 4-6 gradient revealed a multiple-band pattern for each form in the range of pH4.4-4.9. The two forms of rabbit alpha1-antitrypsin possessed the same N-terminal amino acid (glutamic acid) and had very similar amino acid and carbohydrate compositions.
Novel kinetic and structural properties of the class-I D-fructose 1,6-bisphosphate aldolase from Escherichia coli (Crookes' strain)
Authors: Baldwin S A , Perham R N
Published: August 2015

Investigation of aldolase 1, the class-I D-fructose 1,6-bisphosphate aldolase (EC4.1.2.13) from Escherichia coli (Crookes' strain), showed it to have unusual kinetic and structural properties. The enzyme appeared to be larger than was previously supposed and may be a decamer with a mol. wt. of approx. 340000. Its fructose 1,6-bisphosphate-cleavage activity was unaffected by these compounds. The enhancement exhibited a strong dependence on pH. These novel kinetic properties do not seem to be shared by any other fructose 1,6-bisphosphate aldolase, but recall the activation by polycarboxylic acids of the deoxyribose 3-phosphate aldolases from some other organisms. In view of its unusual properties, it is unlikely that aldolase 1 from E. coli is closely related to the class-1 aldolases that have been detected in several other prokaryotes, or to the typical class-1 enzymes from eukaryotes.
The stereochemistry of β-lactam formation in cephalosporin biosynthesis
Authors: Huddleston J A , Abraham E P
Published: August 2015

3H and 14C from (2R,3S)[U-14C,3-3H1]cysteine and (2R,3R)-[U-14C,2,3-3H2]cysteine were incorporated into cephalosporin C by Cephalosporium acremonium. Analysis of the radioactive cephalosporin C indicated that the formation of its beta-lactam ring occurs stereospecifically and with retention of configuration at C-3 of cysteine.