bluuebunny/crossref_metadata_2025 huggingface dataset:
Role of adenosine monophosphate in regulation of metabolic pathways of perfused rat liver
Authors: Hunter A. R. , Jefferson L. S.
Published: August 2015

1. By perfusion of rat livers with 3mm-AMP in the perfusion medium we obtain increased intracellular concentrations of AMP. 2. These high intracellular concentrations of AMP lead to an increased output of glucose and urea into the perfusion medium. 3. The increased output of glucose in livers from fed rats is brought about primarily by an AMP-stimulated breakdown of liver glycogen. In livers from starved rats the increase in glucose output is not as great, reflecting the low contents of glycogen in livers from starved rats. 4. AMP inhibits gluconeogenesis from lactate in perfused livers. In the presence of high concentrations of lactate, however, the counteracting effects of AMP to increase glycogenolysis and to inhibit gluconeogenesis result in little change in the net glucose output. 5. The increased urea output is brought about by increased breakdown of amino acids that are present in the perfusion medium. In livers from starved rats the overall urea production is much higher, indicating increased catabolism of amino acids and other nitrogenous substrates in the absence of carbohydrate substrates. 6. AMP causes an inhibition of incorporation of labelled precursors into protein and nucleic acid. This may result from increased catabolism of precursors of proteins and nucleic acids as reflected by the more rapid breakdown of nitrogenous compounds. In support of this hypothesis, cell-free systems for amino acid incorporation isolated from livers perfused with and without AMP are equally capable of supporting protein synthesis. 7. The labelling pattern of RNA in perfused livers corresponds very closely to those found by pulse-labelling in vivo. AMP in no way alters the qualitative nature of the labelling patterns. 8. We consider these results as supporting evidence for the role of the concentration ratio of AMP to ATP in controlling the metabolic pathways that lead to the formation of ATP.
Metabolism of amino acids in protein-calorie-deficient rats
Authors: McFarlane I. G. , von Holt C.
Published: August 2015

The overall oxidative degradation of leucine and phenylalanine, measured in vivo in rats fed on a 2%-casein diet for 8 weeks, is markedly decreased as compared with controls, whereas that of glutamate and alanine is apparently unaffected. The decrease in leucine degradation is due, at least in part, to a block before the formation of 3-methylbutyryl-CoA (isovaleryl-CoA) in the catabolic pathway. This phenomenon is accompanied by increased incorporation of [14C]leucine into liver proteins, decreased urinary excretion of leucine and increased urinary excretion of 4-methyl-2-oxopentanoate (α-oxoisocaproate) by protein-depleted animals. The results suggest the existence of adaptive mechanisms that function to conserve an indispensable carbon skeleton.
The action of cyanate on human and pig kidney alkaline phosphatases
Authors: Carey M. J. , Butterworth P. J.
Published: August 2015

1. At concentrations of cyanate up to 0·2m there is an apparently reversible combination with alkaline phosphatase (EC 3.1.3.1), but higher concentrations inhibit alkaline phosphatase irreversibly by a process that is time-dependent. 2. The effect of 0·2m-cyanate on the enzymic reaction velocity depends on the substrate concentration. There is inhibition when the substrate concentration is 1·0mm or higher, but at lower substrate concentrations cyanate has an activating effect. 3. The pH-dependence of the reversible reaction suggests that cyanate may react with a thiol group at or near the active site of the enzyme, preventing a conformational change that is believed to be important in the mechanism of action of alkaline phosphatase. 4. Prolonged treatment with 0·6m-cyanate probably carbamoylates all free amino groups in the enzyme molecule and generates a new enzyme with decreased Vmax. and increased Km.
A negative correlation between oxygen uptake and glutathione oxidation in rat liver homogenates
Authors: Pinto R E , Bartley W
Published: August 2015

GSH added to rat liver homogenates inhibited respiration and increased GSSG formation approximately proportionally to the amount of GSH added; the effect was increased by added magnesium chloride. Added NADPH and citrate decreased GSSG formation and increased respiration; 6·0mm-nicotinamide prevented GSSG formation and increased respiration. There was a negative correlation between GSSG formation and oxygen uptake. It is suggested that the decrease in oxygen uptake is mainly due to GSSG concentration and also that in vivo a GSH–GSSG steady state occurs.
Purification and properties of α-d-mannosidase from rat epididymis
Authors: Snaith Sybil M. , Levvy G. A.
Published: August 2015

1. α-d-Mannosidase from rat epididymis was purified 300-fold. β-N-Acetyl-glucosaminidase and β-galactosidase were removed from the preparation by treatment with pyridine. Zn2+ was added during the purification to stabilize the α-mannosidase. 2. Mammalian α-mannosidase is most stable at pH6. At lower pH values it undergoes reversible spontaneous inactivation. The enzyme is also subject to irreversible inactivation, which is delayed by the addition of albumin. 3. Reversible inactivation of α-mannosidase is accelerated by EDTA and reversed or prevented by Zn2+. Other cations, such as Co2+, Cd2+ and Cu2+, accelerate inactivation and the action of a toxic cation can be prevented by Zn2+ or by EDTA in suitable concentration. 4. The enzyme is stabilized by substrate and neither Zn2+, EDTA nor a toxic cation has more than a small effect in the assay of an untreated preparation. The addition of Zn2+ is necessary, however, for a constant rate of hydrolysis during prolonged incubation of the enzyme with substrate. In an EDTA-treated preparation, Zn2+ reactivates the enzyme during the assay. 5. Evidence is presented that α-mannosidase is a dissociable Zn2+–protein complex, in which Zn2+ is essential for enzyme activity.
Immune reactions in polysaccharide media. The composition of the antigen–antibody complexes in the precipitin reaction
Authors: Hellsing Krister
Published: August 2015

The precipitin reaction is enhanced in the presence of polysaccharides (Hellsing, 1966). This reaction has now been studied in detail with labelled antigen (125I-labelled human serum albumin) and antibody (131I-labelled rabbit anti-albumin immunoglobulin G). The relative proportions of antigen and antibody in the precipitates are unchanged by the addition of dextran in spite of the increased precipitation. The ratio of antibody to antigen in the soluble immune complexes decreases with increasing polysaccharide concentration. This can be interpreted as a decrease in the aggregate size of the complexes. At the same time the amount of free antigen in the solution increases. The results are consistent with a decrease in solubility, primarily of the large immune aggregates, together with a shift in the equilibrium between small and large complexes. The effect is in accord with a steric-exclusion phenomenon.
Ultracentrifuge studies of histone fractions from calf thymus deoxyribonucleoprotein
Authors: Edwards P A , Shooter K V
Published: August 2015

Molecular weights and sedimentation coefficients of four major fractions of calf thymus histones were measured. The minimum molecular weights were determined in concentrated solutions of guanidine hydrochloride. The results indicate that, with the possible exception of fraction F3, the fractions are heterogeneous. Comparisons in 0·1m-sodium chloride suggest that fraction F1 does not aggregate and show that fractions F2(a) and F3 aggregate to form larger complexes than does fraction F2(b). The degree of aggregation of each fraction is independent of pH in the range pH1–7. Detailed studies with fraction F2(b) have confirmed that the change in sedimentation coefficient observed as the sodium chloride concentration of the solution is increased results from increases in the apparent molecular weight of the sedimenting units. It has been found that the molecules of fraction F2(b) are present as single molecules only in sodium chloride solutions of 33mm or less. At these low concentrations the effects of charge greatly increase the concentration dependence of the sedimentation rate; the results can, however, be interpreted by using the theory developed by Alexandrowicz & Daniel (1963) and Daniel & Alexandrowicz (1963).
Purification and general properties of δ-aminolaevulate dehydratase from Nicotiana tabacum L.
Authors: Shetty A. S. , Miller G. W.
Published: August 2015

1. δ-Aminolaevulate dehydratase (EC 4.2.1.24) was purified 80-fold from tobacco leaves and its properties were studied. 2. The enzyme had optimum pH7·4 in potassium phosphate buffer, Km6·25×10−4m at 37° and pH7·4, optimum temperature 45° and an activation energy of 11100 cal./mole. 3. The enzyme lost activity when prepared in the absence of cysteine, and this activity was only partly restored by the later addition of thiols. Reagents for thiol groups inactivated the enzyme. 4. Mg2+ was essential for activity, and EDTA and Fe2+ were inhibitory; Mn2+ was an activator or an inhibitor depending on the concentration.
Saturated hydrocarbons in bovine liver
Authors: Nagy Bartholomew , Modzeleski Vincent E. , Scott Ward M.
Published: August 2015

A homologous series of n-alkanes (C14–C33) and two isoprenoid hydrocarbons, 2,6,10,14-tetramethylhexadecane (phytane) and 2,6,10,14-tetramethylpentadecane (pristane) have been identified in bovine liver. Another branched but non-isoprenoid alkane and three isomers of molecular formula C20H40 were partially identified. Phytane and the C18–C22 and C29–C33n-alkanes were found to be the major components in liver, suggesting that at least the main hydrocarbon components were derived from various plants in the diet. The hydrocarbons were separated and identified by a series of steps involving solvent extraction, saponification, elution chromatography on alumina and silica gel columns, molecular sieving and by infrared and ultraviolet spectroscopy, followed by combined capillary gas chromatography–mass spectrometry.
Further observations on the inhibitory effect of extracellular potassium ions on glycine uptake by mouse ascites-tumour cells
Authors: Eddy A A , Hogg M. C.
Published: August 2015

1. The initial rate of uptake of glycine by the tumour cells was measured as a function of the Na+ and K+ concentrations in the solution in which the cells were suspended. When [Gly] was 1mm or 12mm, the rate in the absence of Na+ was independent of [K+] and about 3% or 10% respectively of the rate when [Na+] was 150m-equiv./l. 2. The Na+-dependent glycine entry rate, v, at a given value of [Na+] was successively lowered when [K+] was increased from 8 to 47 to 96m-equiv./l. A kinetic analysis indicated that K+ competitively inhibited the action of Na+. The results were in fair agreement with previous determinations of the kinetic parameters. 3. The presence of 2mm-sodium cyanide and 10mm-2-deoxyglucose lowered the cellular ATP content to less than 3% of the value in the respiring cells. Although v was then about 50% smaller, the relative effects of K+ and Na+ on the system were similar to those observed during respiration. 4. A theoretical analysis indicated that the variation of v with [K+] is not a reliable guide to the extent to which the K+ gradient between the cells and their environment may contribute to the net transport of glycine.
Biochemical and cytological heterogeneity of the differentiating cells of the cellular slime mould Dictyostelium discoideum
Authors: Miller Z. I. , Quance J. , Ashworth J M
Published: August 2015

1. The slug stage of the cellular slime mould Dictyostelium discoideum has been shown to contain two types of cell, which differ in buoyant density. 2. These two cell types also differ in cytological appearance and histochemical behaviour and have very different enzymic activities. 3. Evidence is presented suggesting that the lighter of these two cell types corresponds to cells from the posterior region of the slug (pre-spore cells) and the heavier of the two to cells from the anterior region of the slug (pre-stalk cells).
Properties and biosynthesis of a neurotoxic protein of the venoms of sea snakes Laticauda laticaudata and Laticauda colubrina
Authors: Sato S. , Yoshida H. , Abe H. , Tamiya N.
Published: August 2015

1. A neurotoxic protein similar to erabutoxins a and b of Laticauda semifasciata was isolated in crystalline form from the venoms of Laticauda laticaudata and Laticauda colubrina. The name ‘laticotoxin a’ is proposed. 2. Laticotoxin a is homogeneous by CM-cellulose column chromatography, disc electrophoresis and ultracentrifugation and by terminal amino acid analyses. 3. Laticotoxin a consists of 62 amino acid residues. The molecular weight by ultracentrifuging is 6520. 4. The minimal 50% lethal dose of laticotoxin a by intramuscular injection to mice is 0·13μg./g. body wt. The toxin attacks the postsynaptic membrane, competing with acetylcholine. 5. Radioactive amino acids are incorporated into laticotoxin a in vivo. The incorporation is inhibited by puromycin, suggesting that the biosynthesis of the toxin follows the mechanism of protein biosynthesis, although the toxin molecule is rather small as a protein.
The messenger ribonucleic acid content of Bacillus subtilis 168
Authors: Midgley J. E. M.
Published: August 2015

Bacillus subtilis 168 messenger RNA was determined by DNA–RNA hybridization techniques, with denatured DNA immobilized upon cellulose nitrate membrane filters. The following results were obtained. (1) Cultures of B. subtilis, growing exponentially in enriched glucose–salts medium at 37°, incorporated [5−3H]uracil into both ribosomal and messenger RNA fractions without the kinetic delay expected from the presence of the intracellular nucleotide pools. (2) However short the time of labelling with exogenous labelled uracil (down to 7sec.), 32–36% of the rapidly labelled RNA was messenger RNA and 68–64% was an RNA with the hybridization characteristics of ribosomal RNA. Analysis of the apparent nucleotide base composition of total 32P-labelled rapidly labelled RNA and the two RNA fractions separated by hybridization at a DNA/RNA ratio 5:1 confirmed this finding. Of the rapidly labelled RNA, 31% readily hybridized with DNA at low DNA/RNA ratios and had an apparent base composition like that of the DNA, whereas 69% was hybridized only at low efficiency at low DNA/RNA ratios and had a composition identical with that of ribosomal RNA. (3) In cultures dividing every 48min. at 37°, kinetic analysis of RNA labelled over a 20min. period showed that the average life-time of messenger RNA was 2·7–3·0min. and that its amount was 3·0% of the total RNA. (4) The hybridization of 3H-labelled randomly labelled RNA with DNA at a DNA/RNA ratio 5:1 showed that 2·9% of the randomly labelled RNA had the characteristics of messenger RNA. (5) Experiments carried out as described by Pigott & Midgley (1968) indicated that hybridization at low DNA/RNA ratios (5:1) effectively accounted for all the messenger RNA in a given specimen. The efficiency coefficient of RNA hybridization lay within the range of 90–95% input, if an excess of DNA sites was offered for RNA binding. (6) These measurements are compared with other results obtained by different methods, and reasons for any major disagreement are suggested.
The cellulase of Fusarium solani. Resolution of the enzyme complex
Authors: Wood T. M.
Published: August 2015

1. Culture filtrates from Fusarium solani were fractionated by ion-exchange chromatography on DEAE-Sephadex, followed by gel chromatography on Sephadex G-100, into a C1 component, a Cx component (CM-cellulase) and a β-glucosidase (cellobiase) component. 2. The individual components showed little capacity for the solubilization of cotton fibre (cellulase activity), but when recombined in their original proportions 81% of the original cellulase activity was recovered. 3. The C1 components of F. solani and Trichoderma koningii were similar in their pH optima, heat stabilities over the pH range 5–8 and elution volumes on Sephadex G-100. 4. The C1 component of F. solani synergized with the Cx component of T. koningii and conversely. 5. The C1 and the β-glucosidase components of F. solani were devoid of the swelling-factor (S-factor) activity associated with the Cx component.
Properties of the inactive ribosomal components in rat liver and hepatoma
Authors: Webb Thomas E. , Morris Harold P.
Published: August 2015

1. The relative concentrations of the inactive ribosomal components were compared in normal and regenerating rat liver and in two transplantable rat hepatomas (hepatomas 7800 and 5123D). 2. The size of the ribosomal-subunit pools in normal liver was not significantly affected by partial hepatectomy or neoplasia although, as shown previously, significant changes do occur in the monomer pool. 3. Further, the subunit pools in both liver and hepatoma were not significantly influenced by several treatments that caused dramatic changes in the size of the ribosomal monomer (and dimer) pools. 4. The high concentration of inactive monomers and dimers in the hepatomas appears to arise from limitations at the translational level, since they can be incorporated into pre-existing polyribosomes under the influence of cycloheximide.
The regulation of l-asparaginase activity in rats and mice. Effects of normal and malignant growth, of sex and of dietary changes
Authors: Bonetti E. , Abbondanza Ada , Corte E. Della , Stirpe F.
Published: August 2015

1. The activity of l-asparaginase was very low in the liver of newborn rats and mice, and increased within a few days of birth. 2. In rats, but not in mice, the enzyme activity was higher in females than in males, was enhanced by administration of oestradiol, and was decreased by gonadectomy. 3. The enzyme activity decreased in mice starved or fed on a low-protein diet; in rats it was enhanced by starvation, by feeding them on a high-protein diet, or by administration of l-asparagine. 4. The asparaginase activity was decreased in regenerating liver, and was almost absent in the Morris hepatoma 5123.
The enzymic degradation of ovalbumin and its glycopeptides
Authors: Conchie J. , Hay A J , Strachan I. , Levvy G. A.
Published: August 2015

1. Ovalbumin glycopeptides, freed from all amino acids other than aspartic acid and a small proportion of leucine by repeated digestion with Pronase, were hydrolysed by 1-aspartamido-β-N-acetylglucosamine amidohydrolase (glycoaspartamidase) to the corresponding oligosaccharides. The glycoaspartamidase did not attack ovalbumin itself. 2. Ovalbumin, with mannose/hexosamine ratio 5:4, lost 1·5moles of N-acetylglucosamine and more than 2moles of mannose after incubation with α-mannosidase and β-N-acetylglucosaminidase respectively. 3. In ovalbumin glycopeptides with approximate mannose/hexosamine ratios 5:3 and 5:4, one and two N-acetylglucosamine residues respectively were accessible to the action of β-N-acetylglucosaminidase. 4. A mixture of α-mannosidase and β-N-acetylglucosaminidase, acting on an ovalbumin glycopeptide with mannose/hexosamine ratio 5:3·7, removed nearly 4moles of mannose and 1·5moles of N-acetylglucosamine. 5. α-Mannosidase removed about 1·5moles of mannose from the ovalbumin oligosaccharide with mannose/hexosamine ratio approx. 5:3. The subsequent action of β-N-acetylglucosaminidase liberated less than 1mole of N-acetylglucosamine and made at least 1mole further of mannose accessible to α-mannosidase action. 6. It is concluded that the carbohydrate moiety of ovalbumin is linked through a glycosyl group to asparagine. In a molecule with mannose/hexosamine ratio 5:4, there are two β-N-acetylglucosamine residues linked together in a terminal position, followed by α-mannose. There is also present a side chain containing two α-mannose units.
The importance of life-time changes in fluorescence depolarization
Authors: Johnson P. , Thornton A. C. R.
Published: August 2015

The rotational relaxation time, ρ, calculated from measurements of fluorescence depolarization, is clearly dependent on the assumed mean life-time, τ, of the excited state. However, variations in τ with experimental conditions (temperature and solvent composition) occur and the effect of such alterations in τ is demonstrated. In particular it should be noted that, unless life-time changes can be excluded, the occurrence of linear plots of reciprocal degree of polarization against the temperature/viscosity ratio does not necessarily indicate the absence of intramolecular freedoms. An attempt to correct for such life-time changes by measurement of the fluorescence intensity is made for the bovine serum albumin–1-dimethyl-aminonaphthalene-5-sulphonyl chloride system. The value of ρ/3τ thus obtained for this system at 20° is approx. 4·7, as against approx. 3·4 obtained by several workers in the absence of life-time corrections.
The effect of dietary fat on lipogenesis in mammary gland and liver from lactating and virgin mice
Authors: Smith Stuart , Gagné Harriet T. , Pitelka Dorothy R. , Abraham S.
Published: August 2015

1. Virgin and lactating C3H mice maintained on laboratory chow were transferred to a high-fat (15% corn oil) or a fat-free diet 3 days before being killed. 2. The linoleate content of liver, mammary gland and milk was decreased in lactating mice given the fat-free diet but was increased in those fed on the high-fat diet. Changes in linoleate content and mammary gland followed a similar but much less marked trend in virgin animals. 3. Hepatic fatty acid synthesis in lactating and virgin mice fed on the fat-free diet was higher than in corresponding animals fed on either the chow or the high-fat diet. The lipogenic capacity of livers from mice fed on either the chow or the high-fat diet was greater in lactating than in virgin animals. These changes in hepatic lipogenic capacity were accompanied by alterations in the specific activities of certain enzymes involved in fat synthesis. 4. Mammary gland from virgin and lactating animals showed no such adaptation to dietary fat. Results indicate that fatty acid synthesis in neither mammary-gland parenchymal cells nor mammary-gland adipose cells can be influenced by dietary fat in the same way as in the hepatocyte.
Interaction of solvents with membranal and soluble potassium ion-dependent enzymes
Authors: Mayer M. , Avi-Dor Y.
Published: August 2015

The effects of dimethyl sulphoxide and glycerol on ox brain microsomal Na++K+-stimulated adenosine triphosphatase (EC 3.6.1.3), K+-stimulated p-nitrophenyl phosphatase and K+-dependent muscle pyruvate kinase (EC 2.7.1.40) were studied. Dimethyl sulphoxide at concentrations below 20% (v/v) was found to stimulate the p-nitrophenyl phosphatase and pyruvate kinase by increasing their affinity for K+ but to inhibit the Na++K+-stimulated adenosine triphosphatase. The latter enzyme activity was also inhibited by glycerol, which like dimethyl sulphoxide, stimulated the K+-activated p-nitrophenyl phosphatase at a wide range of concentrations. The solvent effects were promptly reversed by dilution. Similarity was found between glycerol and dimethyl sulphoxide, on one hand, and ATP, on the other, in their stimulatory effect and their ability to increase the ouabain- and oligomycin-sensitivity of the K+-stimulated p-nitrophenyl phosphatase. However, only the solvents, not the ATP, increased the binding of K+ by the microsomes. From the above findings it is suggested that solvents may act on K+-dependent enzymes by altering the state of solvation of the activating cation as well as by changing the enzyme structure.
Metabolism of endogenous sterol ester by the superovulated rat ovary in vitro
Authors: Flint A. P. F. , Denton R. M.
Published: August 2015

Sterol, glyceride and phospholipid were found to account for more than 90% (w/w) of the lipid extracted from whole superovulated rat ovaries. These lipids, together with non-esterified fatty acids, were assayed in slices of the tissue after incubation for various times. Whereas the concentrations of triglyceride, diglyceride and phospholipid did not change significantly during incubation, that of sterol ester markedly decreased and those of free sterol, monoglyceride and non-esterified fatty acid increased. Evidence is presented that in this tissue (in contrast with other mammalian tissues) the main endogenous substrate for respiration is fatty acid derived from sterol ester.
Alternative pathways of spirilloxanthin biosynthesis in Rhodospirillum rubrum
Authors: Davies B. H.
Published: August 2015

Detailed studies of the properties of carotenoids isolated from diphenylamine-inhibited cultures of Rhodospirillum rubrum have revealed a number of novel structures that indicate new features of carotenoid biosynthesis in the photosynthetic bacteria. Both neurosporene and 7,8,11,12-tetrahydrolycopene undergo hydration, methylation and dehydrogenation to yield spheroidene and 11′,12′-dihydrospheroidene respectively; all the intermediates in these pathways have been identified. These pathways represent alternative routes of anhydrorhodovibrin and spirilloxanthin biosynthesis.
The fractionation of dinucleoside monophosphate and some trinucleoside diphosphate isonicotinoyl hydrazones by column chromatography
Authors: Hunt John A.
Published: August 2015

A column-chromatographic system using DEAE-cellulose and gradient elution with triethylammonium formate at pH4.0–3.5 is described. It is capable of separating the oligonucleotide isonicotinoyl hydrazones that are produced by nuclease digestion of RNA oxidized with periodate and coupled with isonicotinic acid hydrazide. Fifteen dinucleoside monophosphate isonicotinoyl hydrazones were characterized by their elution positions on the columns, so that all but two of them could readily be identified. Twelve trinucleoside diphosphate hydrazones were also characterized by their elution positions on the column. The application of this method of fractionation to terminal-sequence studies of RNA is discussed.
Protocollagen proline hydroxylase of the mouse uterus during pregnancy and post-partum involution
Authors: Halme Jouko , Jääskeläinen Marketta
Published: August 2015

1. The protocollagen proline hydroxylase in mouse uterus was found to be similar to that in other animal sources in its subcellular distribution and cofactor requirements. 2. The activities of this enzyme in uterine tissue from non-pregnant mice were comparable with those in various embryonic tissues. 3. In the second half of pregnancy the protocollagen proline hydroxylase activity increased markedly. 4. After parturition the activity of this enzyme decreased rapidly, reaching normal non-pregnant values at 24h post partum. The results suggest a good correlation between the synthesis of collagen and the activity of protocollagen proline hydroxylase.
Changes in proton-magnetic-resonance spectra during aminolysis and enzymic hydrolysis of cephalosporins
Authors: Hamilton-Miller J. M. T. , Richards Eva , Abraham E. P.
Published: August 2015

1. Changes in proton-magnetic-resonance spectra were followed during the reaction of cephalosporins, deacetylcephalosporins, deacetoxycephalosporins and a Δ2-cephalosporin with ND3 in D2O. 2. Changes in proton-magnetic-resonance spectra were also followed during the hydrolysis of a cephalosporin and a deacetylcephalosporin in D2O with a β-lactamase. 3. Structures for the reaction products are proposed. 4. The signals obtained after aminolysis of the β-lactam ring of a cephalosporin indicate that the reaction is accompanied by expulsion of the acetoxy group as acetate, formation of a double bond in the Δ4-position and the appearance of an exocyclic methylene group. 5. Aminolysis of deacetyl- and deacetoxycephalosporins can occur without immediate structural changes in the dihydrothiazine ring. 6. In contrast, the ring structure of the first product of enzymic hydrolysis of a deacetylcephalosporin is apparently identical with that of the product of aminolysis of the cephalosporin itself.
Evidence for the absence of the terminal adenine nucleotide at the amino acid-acceptor end of transfer ribonucleic acid in non-lactating bovine mammary gland and its inhibitory effect on the aminoacylation of rat liver transfer ribonucleic acid
Authors: Herrington M. D. , Hawtrey A. O.
Published: August 2015

1. tRNA isolated from non-lactating bovine mammary gland competitively inhibits the formation of aminoacyl-tRNA in the rat liver system. 2. Non-lactating bovine mammary gland tRNA and twice-pyrophosphorolysed rat liver tRNA are unable to accept amino acids in a reaction catalysed by aminoacyl-tRNA synthetases from either rat liver or bovine mammary gland. Deacylated rat liver tRNA can however be aminoacylated in the presence of either enzyme. 3. Bovine mammary gland tRNA lacks the terminal adenine nucleotide at the 3′-terminus amino acid acceptor end, which can be replaced by incubation in the presence of rat liver nucleotide-incorporating enzyme, ATP and CTP. 4. The enzymically modified bovine tRNA (tRNApCpCpA) can bind labelled amino acids to form aminoacyl-tRNA, which can then transfer its labelled amino acids to growing polypeptide chains on ribosomes. 5. Molecules of rat liver tRNA or bovine mammary gland tRNA that lack the terminal adenine nucleotide or the terminal cytosine and adenine nucleotides inhibit the aminoacylation of normal rat liver tRNA to varying degrees. tRNA molecules lacking the terminal -pCpCpA nucleotide sequence exhibit the major inhibitory effect. 6. The enzyme fraction from bovine mammary gland corresponding to that containing the nucleotide-incorporating enzyme in rat liver is unable to catalyse the incorporation of cytosine and adenine nucleotides in pyrophosphorolysed rat liver tRNA and deacylated bovine tRNA. This fraction also markedly inhibits the action of the rat liver nucleotide-incorporating enzyme.
Comparative studies of bile salts. 5α-Chimaerol, a new bile alcohol from the white sucker Catostomus commersoni Lacépède
Authors: Anderson I. G. , Haslewood G. A. D.
Published: August 2015

1. G.l.c. examination of bile alcohols prepared from the sucker Catostomus commersoni Lacépède (family Catostomidae) showed that although 5α-cyprinol (5α-cholestane-3α,7α,12α,26,27-pentol) was a minor constituent, the principal bile alcohol was an undescribed substance, probably present in the bile as the C-26 sulphate ester, whose i.r., n.m.r. and mass spectra agreed with the structure 5α-cholestane-3α,7α,12α,24,26-pentol. 2. MD studies suggest that this 5α-chimaerol is the 24(+), 25S enantiomer and that 5β-chimaerol (chimaerol) from Chimaera monstrosa bile also has the 24(+), 25S configuration. These findings imply that bile alcohol biosynthesis in suckers and chimaeras includes stereospecific oxidation of cholesterol at C-26. 3. C. commersoni bile acids (present in minor amounts) probably consist largely of 3α,7α,12α-trihydroxy-5α-cholan-24-oic acid (allocholic acid). 4. 5α-Chimaerol sulphate and 5α-cyprinol sulphate are probably biochemically equivalent as bile salts, and can be considered as arising by parallel evolution.
Co-ordination between membrane phospholipid synthesis and accelerated biosynthesis of cytoplasmic ribonucleic acid and protein
Authors: Tata J. R.
Published: August 2015

1. The rate of synthesis of membrane phospholipid was studied in rat liver and seminal vesicles by following the incorporation of [32P]orthophosphate, [14C]choline and [14C]glycerol. Particular emphasis was laid on the endoplasmic reticulum, which was fractionated into smooth microsomal membranes, heavy rough membranes, light rough membranes and free polyribosomes. 2. Phospholipid labelling patterns suggested a heterogeneity in the synthesis and turnover of the different lipid moieties of smooth and rough endoplasmic membranes. The major phospholipids, phosphatidylcholine and phosphatidylethanolamine, were labelled relatively rapidly with 32P over a short period of time whereas incorporation of radioisotope into the minor phospholipids, sphingomyelin, lysolecithin and phosphatidylinositol proceeded slowly but over a longer period of time. 3. The incorporation of orotic acid into RNA and labelled amino acids into protein of the four submicrosomal fractions was also studied. 4. Rapid growth of the liver was induced by the administration of growth hormone and tri-iodothyronine to hypophysectomized and thyroidectomized rats and by partial hepatectomy. Growth of seminal vesicles of castrated rats was stimulated with testosterone propionate. 5. The rate of labelling of membrane phospholipids was enhanced in all major subcellular particulate fractions (nuclear, mitochondrial and microsomal) during induced growth. However, it was in the rough endoplasmic reticulum that the accumulation of phospholipids, RNA and protein was most marked. The effect of hormone administration was also to accelerate preferentially the labelling with 32P of sphingomyelin relative to that of phosphatidylcholine or phosphatidylethanolamine. 6. Time-course analyses showed that, in all four growth systems studied, the enhancement of the rate of membrane phospholipid synthesis coincided with the rather abrupt increase in the synthesis of RNA and protein of the rough endoplasmic reticulum. Growth hormone and tri-iodothyronine administered to hypophysectomized rats had additive effects in all the biosynthetic processes. The latent period of action of each hormone was maintained so that two waves of proliferation of endoplasmic reticulum occurred if the hormones were administered simultaneously. 7. It is concluded that there is some mechanism in the cell that tightly co-ordinates the formation of membranes, especially those of the endoplasmic reticulum, when an increased demand is made for protein synthesis.
Variations in the activity of several enzymes in the mammary glands of non-pregnant, pregnant and lactating rabbits
Authors: Hartmann P. E. , Jones E. A.
Published: August 2015

1. The enzymes phosphofructokinase (EC 2.7.1.11), 6-phosphogluconate dehydrogenase (EC 1.1.1.44), phosphoglucomutase (EC 2.7.5.1), ATP–citrate lyase (EC 4.1.3.8), acetyl-CoA carboxylase (EC 6.4.1.2) and acetyl-CoA synthetase (EC 6.2.1.1) were assayed in rabbit mammary glands at various stages of the pregnancy–lactation cycle. 2. The activities of all enzymes were low during pregnancy and, with the exception of phosphofructokinase, in non-pregnant animals. Two- to ten-fold increases in enzyme activities occurred over the first 20 days of lactation. Although milk yield was considerably decreased, the enzyme activities remained elevated in late lactation (45 days after parturition). 3. These findings are discussed in relation to mammary-gland metabolism and compared with similar observations previously made on ruminants and other small mammals.
Role of liver-cell potassium ions in secretion of serum albumin and lipoproteins
Authors: Judah J. D. , Nicholls Marion R.
Published: August 2015

1. The incorporation of l-[1-14C]leucine into the proteins of liver slices and into the serum albumin and lipoproteins transported by these slices was investigated. 2. Transport rates were found to be dependent on the K+ content of the slices. 3. The effect of K+ on transport of serum albumin and of serum lipoprotein can be separated from any effect on synthesis by altering K+ concentrations after inhibition of protein synthesis by cycloheximide or puromycin. 4. The effect of low K+ concentrations is reversible. 5. There is linear relationship between the K+ content of the slices and the transport of protein. A simple method is described for maintaining various steady concentrations of K+ in the liver slices. 6. K+ may be replaced by Rb+. Cs+ is partly effective, but NH4+ and Li+ are no more effective than Na+. 7. We found evidence that K+ content rather than the flux rates of K+ or Na+ is important in this effect. 8. These results are probably important in ethionine and carbon tetrachloride poisoning in the rat, and may be significant in liver transplantation.
A reinvestigation of residues 64–68 and 175 in papain. Evidence that residues 64 and 175 are asparagine
Authors: Husain S. S. , Lowe G.
Published: August 2015

The tryptophan-containing peptides were isolated from the chymotryptic digest of S-carboxymethylated papain. Residue 175, which is strongly hydrogen-bonded to the active-site histidine residue in the tertiary structure of papain, is asparagine, confirming the work of Kimmel, Rogers & Smith (1965). Its function is probably to maintain the orientation and tautomeric state of the imidazole ring of histidine-159. The amino acid sequence predicted from the electron-density map of papain for residues 64–68 was confirmed, but residue 64 is asparagine, not aspartic acid. This residue, which is about 10 Å from the thiol group of the active-site cysteine-25, cannot therefore be a site of electrostatic attraction for substrates of basic amino acids.
Separation of antigens by immunological specificity. Studies on the desorption of homologous antigen from disulphide-linked antibody immunosorbents
Authors: Chidlow J. W. , Stephen J. , Smith H.
Published: August 2015

1. Glycine–hydrochloric acid buffer, pH2.2, desorbed 131I-labelled human serum albumin (100%), lysozyme (100%), ovalbumin (90%), fluorescent ovalbumin (50–60%) and fluorescent human γ-globulin (20%) from their respective homologous disulphide-linked antibody immunosorbents; reasons are suggested for the low recoveries of the fluorescently labelled proteins. 2. Approx. 40% of the recovered 131I-labelled human serum albumin and fluorescent ovalbumin was desorbed above pH6.0, but lysozyme was not eluted until the pH was 3.0 or below. 3. In all cases where high recoveries of antigen were obtained, the immunosorbents could be regenerated and recycled at least four times with full retention of specificity and minimal diminution of capacity. 4. The desorbed antigens were unchanged when compared with the original antigens by quantitative precipitin, specificradioactivity, fluorescent and enzymic analyses and by cellulose acetate electrophoresis. 5. Desorption of antigen with a variety of reagents was investigated. These reagents were less satisfactory than glycine–hydrochloric acid.
The role of nicotinamide–adenine dinucleotide phosphate-dependent malate dehydrogenase and isocitrate dehydrogenase in the supply of reduced nicotinamide–adenine dinucleotide phosphate for steroidogenesis in the superovulated rat ovary
Authors: Flint A. P. F. , Denton R. M.
Published: August 2015

1. Superovulated rat ovary was found to contain high activities of NADP–malate dehydrogenase and NADP–isocitrate dehydrogenase. The activity of each enzyme was approximately four times that of glucose 6-phosphate dehydrogenase and equalled or exceeded the activities reported to be present in other mammalian tissues. Fractionation of a whole tissue homogenate of superovulated rat ovary indicated that both enzymes were exclusively cytoplasmic. The tissue was also found to contain pyruvate carboxylase (exclusively mitochondrial), NAD–malate dehydrogenase and aspartate aminotransferase (both mitochondrial and cytoplasmic) and ATP–citrate lyase (exclusively cytoplasmic). 2. The kinetic properties of glucose 6-phosphate dehydrogenase, NADP–malate dehydrogenase and NADP–isocitrate dehydrogenase were determined and compared with the whole-tissue concentrations of their substrates and NADPH; NADPH is a competitive inhibitor of all three enzymes. The concentrations of glucose 6-phosphate, malate and isocitrate in incubated tissue slices were raised at least tenfold by the addition of glucose to the incubation medium, from the values below to values above the respective Km values of the dehydrogenases. Glucose doubled the tissue concentration of NADPH. 3. Steroidogenesis from acetate is stimulated by glucose in slices of superovulated rat ovary incubated in vitro. It was found that this stimulatory effect of glucose can be mimicked by malate, isocitrate, lactate and pyruvate. 4. It is concluded that NADP–malate dehydrogenase or NADP–isocitrate dehydrogenase or both may play an important role in the formation of NADPH in the superovulated rat ovary. It is suggested that the stimulatory effect of glucose on steroidogenesis from acetate results from an increased rate of NADPH formation through one or both dehydrogenases, brought about by the increases in the concentrations of malate, isocitrate or both. Possible pathways involving the two enzymes are discussed.
Study of the thermal denaturation of ribonuclease A by differential thermal analysis and susceptibility to proteolysis
Authors: Winchester B. G. , Mathias A. P. , Rabin B. R.
Published: August 2015

1. The thermally induced change in conformation of ribonuclease A in solution was investigated by differential thermal analysis and the susceptibility of the enzyme to proteolytic digestion by ficin. 2. A transition with a mid-point of 60.5°C at pH4.2 was observed directly by differential thermal analysis and shown to be a property of the native structure. 3. At pH4.2 ribonuclease A is susceptible to ficin digestion at 60°C but not at 18°C. 4. Chromatographic analysis of the digestion products reveals that transient active intermediates are produced during the digestion. 5. Three of these intermediates were purified and partially characterized. 6. The nature of those sections of the ribonuclease molecule that are involved in the thermal transition is discussed.
Rat small-intestinal β-galactosidases. Studies on the fractionation of ‘acid’ β-galactosidase with isoelectric focusing, gel filtration and ion-exchange chromatography
Authors: Asp Nils-Georg
Published: August 2015

1. Different forms of the rat small-intestinal ‘acid’ β-galactosidase were separated by using the isoelectric-focusing technique. The isoelectric points of the different forms were at pH4.2, 4.6, 5.4, 6.1 and approx. 8. 2. The two forms of ‘acid’ β-galactosidase isoelectric at pH4.2 and 4.6 were completely excluded from the Sephadex G-200 gel, whereas the form isoelectric at pH8 had Kav. 0.4. The concentration and pH of the elution buffer influenced the distribution of enzyme activity between different forms. Thus, under certain conditions of ionic strength and pH, the enzyme seems to form high-molecular-weight aggregates with low isoelectric points. These may be homopolymeric aggregates or the result of binding of enzyme to, for example, membrane fragments. The forms isoelectric at pH5.4 and 6.1 are probably aggregates of intermediate size. 3. During ion-exchange chromatography at pH6.0 one fraction of ‘acid’ β-galactosidase was not retained on the column and was isoelectric at pH8 and another fraction was eluted when the buffer concentration in the eluate had increased to about 50mm. The main part of enzyme eluted in this second fraction was also isoelectric at pH8, indicating that the elution of this fraction is not a simple ion-exchange procedure but probably also involves a splitting of high-molecular-weight aggregates, originally retained because of their low isoelectric points. The enzyme subunits have a higher isoelectric point, and are therefore no longer bound to the ion-exchange resin.
The interaction of fetuin with phosphatidylcholine monolayers. Characterization of a lipoprotein membrane system suitable for the attachment of myxoviruses
Authors: Tiffany J. M. , Blough H. A.
Published: August 2015

1. An artificial membrane system was formed by spreading at air/water and oil/water interfaces, by using phosphatidylcholine and the glycoprotein fetuin (mol.wt. 48400). 2. The plot of increase of interfacial pressure against amount of protein added beneath a monomolecular film of phosphatidylcholine showed two discontinuities, corresponding to the completion of two distinct layers of protein: (a) largely denatured and closely associated with the polar head groups of phosphatidylcholine, possibly with penetration of non-polar protein groups between the phosphatidylcholine molecules and (b) an additional adsorbed layer of substantially native fetuin in either a close-packed or open-lattice array. A more compactly organized membrane was apparently formed at pH7.4 with 1mm-Mg2+ in the aqueous phase than without Mg2+; at 15mm-Mg2+, more random adsorption of protein appeared to take place. Qualitatively similar results were obtained at pH5.1 with 1mm-Mg2+. Closer initial packing of the phosphatidylcholine layer decreased both the magnitude of the interfacial pressure change and the amounts of protein bound in the two layers. 3. The amount of N-acetylneuraminic acid released by neuraminidase (EC 3.2.1.18) in the subphase was measured at pH5.1; a mean distribution of 9.7×1013 residues/cm2 was calculated for the completed second protein layer.
Biosynthesis of amino acids in Clostridium pasteurianum
Authors: Dainty R. H. , Peel J. L.
Published: August 2015

1. Clostridium pasteurianum was grown on a synthetic medium with the following carbon sources: (a) 14C-labelled glucose, alone or with unlabelled aspartate or glutamate, or (b) unlabelled glucose plus 14C-labelled aspartate, glutamate, threonine, serine or glycine. The incorporation of 14C into the amino acids of the cell protein was examined. 2. In both series of experiments carbon from exogenous glutamate was incorporated into proline and arginine; carbon from aspartate was incorporated into glutamate, proline, arginine, lysine, methionine, threonine, isoleucine, glycine and serine. Incorporations from the other exogenous amino acids indicated the metabolic sequence: aspartate → threonine → glycine ⇌ serine. 3. The following activities were demonstrated in cell-free extracts of the organism: (a) the formation of aspartate by carboxylation of phosphoenolpyruvate or pyruvate, followed by transamination; (b) the individual reactions of the tricarboxylic acid route to 2-oxoglutarate from oxaloacetate; glutamate dehydrogenase was not detected; (c) the conversion of aspartate into threonine via homoserine; (d) the conversion of threonine into glycine by a constitutive threonine aldolase; (e) serine transaminase, phosphoserine transaminase, glycerate dehydrogenase and phosphoglycerate dehydrogenase. This last activity was abnormally high. 4. The combined evidence indicates that in C. pasteurianum the biosynthetic role of aspartate and glutamate is generally similar to that in aerobic and facultatively aerobic organisms, but that glycine is synthesized from glucose via aspartate and threonine.
Enzymes of Trichomonas foetus. Separation and properties of two β-galactosidases
Authors: Harrap G. J. , Watkins Winifred M.
Published: August 2015

The β-galactosidase activity in extracts of Trichomonas foetus is separable into two fractions by gel filtration on Sephadex G-200. When o-nitrophenyl β-d-galactoside is used as substrate the first fraction to be eluted, β-galactosidase 1, has 50 times the activity (units per mg of protein) of the crude preparation. This fraction is activated by Mn2+ and Co2+ and inhibited by Hg2+ and EDTA. In the presence of Mn2+ the pH optimum for the hydrolysis of o-nitrophenyl β-d-galactoside or lactose is 5.8–6.0. β-Galactosidase 1 is an exoglycosidase that releases β-linked galactose joined to aliphatic and various carbohydrate aglycones. Hydrolysis is prevented, however, by a substituent on either the subterminal sugar or the terminal non-reducing β-galactosyl residue in an oligosaccharide. The second fraction, β-galactosidase 2, is not activated by metal ions or inhibited by EDTA and has a broad pH optimum from 4.5 to 6.0.