bluuebunny/crossref_metadata_2025 huggingface dataset:
Streptomyces natalensis programmed cell death and morphological differentiation are dependent on oxidative stress
Authors: Beites Tiago , Oliveira Paulo , Rioseras Beatriz , Pires Sílvia D. S. , Oliveira Rute , Tamagnini Paula , Moradas-Ferreira Pedro , Manteca Ángel , Mendes Marta V.
Published: August 2015

Streptomyces are aerobic Gram-positive bacteria characterized by a complex life cycle that includes hyphae differentiation and spore formation. Morphological differentiation is triggered by stressful conditions and takes place in a pro-oxidant environment, which sets the basis for an involvement of the oxidative stress response in this cellular process. Characterization of the phenotypic traits of Streptomyces natalensis ΔkatA1 (mono-functional catalase) and ΔcatR (Fur-like repressor of katA1 expression) strains in solid medium revealed that both mutants had an impaired morphological development process. The sub-lethal oxidative stress caused by the absence of KatA1 resulted in the formation of a highly proliferative and undifferentiated vegetative mycelium, whereas de-repression of CatR regulon, from which KatA1 is the only known representative, resulted in the formation of scarce aerial mycelium. Both mutant strains had the transcription of genes associated with aerial mycelium formation and biosynthesis of the hyphae hydrophobic layer down-regulated. The first round of the programmed cell death (PCD) was inhibited in both strains which caused the prevalence of the transient primary mycelium (MI) over secondary mycelium (MII). Our data shows that the first round of PCD and morphological differentiation in S. natalensis is dependent on oxidative stress in the right amount at the right time.
Characterization of Nanomaterials Using Transmission Electron Microscopy
Authors: Smith David J.
Published: August 2015

The transmission electron microscope (TEM) is the perfect instrument for structural and chemical characterization at the nanoscale. Imaging, diffraction and microanalytical information are easily produced and then combined to give detailed insights into the properties and behavior of nanostructured materials. This chapter begins with an introduction to imaging modes and several other important aspects of high-resolution imaging, including the development of aberration correction for electron microscopy. Typical examples ranging from nanoparticles to quantum wells, nanowires and quantum dots are then briefly described to illustrate the diverse range of applications of the TEM to studying nanomaterials. Finally, emerging trends and practical concerns that continue to impact the success of electron microscopy studies are briefly discussed.
Hydrophilic modification of titania nanomaterials as a biofunctional adsorbent for selective enrichment of phosphopeptides
Authors: Liu Hailong , Yang Tianyi , Dai Junyong , Zhu Jiayu , Li Xiaoran , Wen Rui , Yang Xinghao
Published: August 2015

Developing an approach to prepare more efficient TiO2-based MOAC nanomaterials for phosphoproteome research.
The cytotoxicity of gold nanoparticles is dispersity-dependent
Authors: Huang Dengtong , Zhou Hualu , Liu Hanyu , Gao Jinhao
Published: August 2015

Well-dispersed gold nanoparticles show rather good biocompatibility, while aggregated gold nanoparticles with the same dose show considerable cytotoxicity. This result indicates that the dispersity of nanoparticles plays an important role in cytotoxicity.
Synthesis of 2-arylbenzimidazoles under mild conditions catalyzed by a heteropolyacid-containing task-specific ionic liquid and catalyst investigation by electrospray (tandem) mass spectrometry
Authors: Alvim Haline G. O. , de Oliveira Heibbe C. B. , Bataglion Giovana A. , Eberlin Marcos N. , Ramos Luciana M. , Silva Wender A.
Published: August 2015

A task-specific ionic liquid constituted by a Bronsted acid (1-(3-sulfopropyl)-3-methyl-imidazolium hydrogen sulfate), namely MSI, and by [PW12O40]3−, namely PW, was used for the condensation reaction in the synthesis of 2-arylbenzimidazoles.
Fabrication of nanocomposites by covalent bonding between noble metal nanoparticles and polymer matrix
Authors: Iwan M. , Andryszewski T. , Wydryszek M. , Fialkowski M.
Published: August 2015

Noble metal nanoparticles capped with novel aminothioalkil ligands are used to fabricate polymer nanocomposites. The nanoparticles are permanently attached to the polymer matrix through covalent bonding.
Fluorescent crystals and co-crystals of 1,8-naphthalimide derivatives: synthesis, structure determination and photophysical characterization
Authors: Grepioni F. , d'Agostino S. , Braga D. , Bertocco A. , Catalano L. , Ventura B.
Published: August 2015

Fluorescent crystals were obtained by solid-state co-crystallization of 4-pyperidinyl-1,8-naphthalimide derivatives with a halogenated co-former.
Effect of chloramphenicol on ribonucleic acid synthesis in liver cells in suspension
Authors: Jacob ST , Bhargava PM
Published: August 2015

1. Chloramphenicol has a stimulatory effect on the incorporation of radioactive phosphate into the RNA of perfused rat-liver slices, whole liver homogenates or the liver-cell suspensions, and no effect on the incorporation of [(14)C]adenine and [(14)C]uracil into the RNA of the tissue slices. 2. Chloramphenicol completely inhibits the incorporation of labelled adenine and uracil into the RNA of the cell suspensions, or into the RNA of homogenates derived from the whole liver tissues. 3. Chloramphenicol has at most a slight inhibitory effect on the transport of labelled adenine or uracil in the hepatic cells in suspension; in the slices, the transport of these bases is not inhibited at all. 4. The above observations indicate that: (a) unlike the tissue slices, hepatic cells in suspension are permeable to chloramphenicol; (b) in the presence of chloramphenicol, for reasons that are not clear, the conversion of the base into the appropriate nucleotide does not proceed.
Homogeneity studies on human growth hormone
Authors: Hunter WM
Published: August 2015

1. Human growth hormone preparations (Raben) have been found to contain 10-40% of denatured growth hormone as shown by radioimmunoassay, reaction of radioiodinated subfractions with antiserum to whole growth hormone, and amino acid analysis, and confirmed by bioassay using the tibia test. 2. The altered fraction was more electronegative than the intact hormone on starch-grain electrophoresis in barbitone buffer, pH8.6. Some heterogeneity of the active material was detectable in simple buffer extracts of a single acetone-stored pituitary gland. 3. The inert fraction was more completely separated from the active hormone as an unretarded fraction from Sephadex G-200 columns with a borate buffer. This separation was due to aggregation of the denatured growth hormone in borate buffer. The active fraction from the Sephadex column still contained some inert material and the amount of this remaining varied considerably between different batches of growth hormone. 4. The radioimmunoassay procedure detects only the immunologically and biologically intact fraction.
The connexion between active cation transport and metabolism in erythrocytes
Authors: Whittam R , Ager ME
Published: August 2015

1. A study has been made of the dependence on the concentrations of internal Na(+) and external K(+) of lactate and phosphate production in human erythrocytes. 2. Lactate production was stimulated by Na(+) and K(+) but only when they were internal and external respectively. The stimulation was counteracted by ouabain. The production of phosphate was affected in the same way. 3. There is a quantitative correlation between these effects and those previously found for cation movements and the membrane adenosine triphosphatase. 4. It is concluded that the rate of energy production in glycolysis is partly controlled by the magnitude of active transport; the extent of this regulation is shown to vary from 25 to 75% of a basal rate that is independent of active transport. 5. The activity of the membrane adenosine triphosphatase was also compared with rates of Na(+) and K(+) transport. The latter were varied by altering the concentrations of internal Na(+) and external K(+), and by inhibiting with ouabain. 6. A threefold variation of active transport rate was accompanied by a parallel change in the membrane adenosine-triphosphatase activity. The results show a constant stoicheiometry for the number of ions moved/mol. of ATP hydrolysed, independent of the electrochemical gradient against which the ions were moved. 7. Calculations show that the amount of ATP hydrolysed would provide enough energy for the osmotic work. The results are discussed in relation to possible mechanisms for active transport.
Studies on bone enzymes. The assay of acid hydrolases and other enzymes in bone tissue
Authors: Vaes G , Jacques P
Published: August 2015

1. Nine acid hydrolases, cytochrome oxidase, alkaline phenylphosphatase and catalase were demonstrated in 0.25m-sucrose homogenates of newborn-rat calvaria. The acid hydrolases were: acid phenylphosphatase, acid beta-glycerophosphatase, beta-glucuronidase, beta-N-acetylglucosaminidase (beta-N-acetylaminodeoxyglucosidase), acid ribonuclease and acid deoxyribonuclease, showing optimum activity at about pH5; cathepsin, beta-galactosidase and hyaluronidase, with optimum activity at about pH3.6. 2. The main kinetic characters of these enzymes have been studied and methods for their quantitative assay have been worked out. The activities present in bone are given and compared with those found in liver. 3. Acid-phosphatase activity was assayed with phenyl phosphate and beta-glycerophosphate as substrates: activities with these two substrates appeared to be due to two different enzymes. Acid phenylphosphatase is particularly labile and is readily inactivated by various physical or chemical agents.
Regulation of ascorbic acid and of xylulose synthesis in rat-liver extracts. The effect of alloxan-diabetes on the glucuronic acid pathway
Authors: Stirpe F , Comporti M
Published: August 2015

1. The synthesis of l-ascorbic acid and of l-xylulose from d-glucuronolactone, d-glucuronate, l-gulonate and l-gulonolactone has been studied with liver extracts from normal and alloxan-diabetic rats. 2. In diabetic animals the synthesis of ascorbic acid is impaired, and more from glucuronolactone and glucuronate than from gulonate and gulonolactone, whereas the formation of xylulose from gulonate and gulonolactone is enhanced. These changes are reversed by insulin therapy. 3. The activity of the NAD-linked gulonate dehydrogenase is enhanced during diabetes.
Spectrophotometric measurement of the liberation of the α-amino group of cysteine residues in polypeptides
Authors: Streichman S , Avi-Dor Y
Published: August 2015

1. The reaction between beta-bromopyruvic acid and SH groups of cysteine residues in reduced ribonuclease and in some other polypeptides was investigated. 2. One molecule of the acid was found to be necessary to block one SH group in reduced ribonuclease. The stoicheiometry of the interaction and the spectral characteristics of the compound formed suggested that the product is and S-oxalomethyl (R.S.CH(2).CO.CO(2)H) derivative of reduced ribonuclease. 3. Digestion of reduced S-oxalomethylated ribonuclease by trypsin or chymotrypsin induced changes in the spectrum that could be attributed to the liberation of the alpha-amino group of S-oxalomethylated cysteine residues from peptide bonds. The spectral changes that accompanied the hydrolysis of specific peptide bonds in reduced S-oxalomethylated ribonuclease and S-oxalomethylated co-poly(l-Lys,l-CySH) allowed the kinetics of the digestion to be followed. 4. Possible applications of the spectrophotometric method in the study of protein structure are discussed.
Purine-phosphoribosyltransferase activities in rat and mouse tissues and in Ehrlich ascites-tumour cells
Authors: Murray AW
Published: August 2015

1. The activities of adenine phosphoribosyltransferase and hypoxanthine phosphoribosyltransferase in extracts of rat and mouse liver, brain, spleen, heart and kidney, of rat bone marrow and of Ehrlich ascites-tumour cells have been measured. The specific activity of adenine phosphoribosyltransferase in tumour cells (3mmu-moles of nucleotide formed/min./mg. of protein) was between 15 and 60 times the activity of any mouse tissue examined. Hypoxanthine-phosphoribosyltransferase activity was greater in extracts of tumour cells than in mouse tissues, but the difference was not great. 2. The specific activities of both adenine phosphoribosyltransferase and hypoxanthine phosphoribosyltransferase in ascites-tumour cells decreased respectively by 57% and 36% 2 days after the cells had been inoculated into mice. After 4 days of tumour growth the specific activities of both enzymes increased, reaching a maximum at 10 days. 3. The activity of adenine phosphoribosyltransferase in rat-liver extracts increased steadily up to 4 days after partial hepatectomy, and was still above the control value after 14 days. Hypoxanthine-phosphoribosyltransferase activity in extracts of regenerating rat liver did not increase until the second day after operation and had begun to decrease by the fourth day. 4. From the results it was concluded that adenine phosphoribosyltransferase and hypoxanthine phosphoribosyltransferase may be physiologically important enzymes in rapidly growing tissues, and that inhibitors of the former enzyme have potential value in chemotherapy.
Substrate and inhibitor specificity of the cholesterol oxidase in bovine adrenal cortex
Authors: Raggatt PR , Whitehouse MW
Published: August 2015

1. Cholesteryl 3beta-sulphate is oxidized in vitro by preparations of bovine adrenal-cortex mitochondria to pregnenolone sulphate and isocaproic acid (4-methyl-pentanoic acid) without hydrolysis of the ester linkage. 2. Free cholesterol is the preferred substrate for adrenal-cortex cholesterol oxidase; the apparent K(m) for cholesteryl sulphate is 500mum and for free cholesterol 50mum under the same conditions. 3. Cholesteryl 3beta-acetate is hydrolysed by bovine adrenal-cortex mitochondria in vitro to free cholesterol, which is subsequently oxidized to more polar steroids and isocaproic acid. Evidence was obtained that other cholesterol esters behave similarly. Cholesterol esters may thus act as precursors of steroid hormones. 4. Cholest-4-en-3-one is only poorly oxidized to isocaproic acid and more polar steroids and thus is probably not a significant precursor of steroid hormones. 5. Cholesteryl esters inhibit the oxidation of cholesterol competitively (K(i) for cholesteryl phosphate 28mum, for cholesteryl sulphate 110mum, for cholesteryl acetate 65mum) but pregnenolone esters do not inhibit this system. 6. Pregnenolone and 20alpha-hydroxycholesterol (both metabolites of cholesterol in this system) inhibit the oxidation of cholesterol non-competitively. K(i) for pregnenolone is 130mum and K(i) for 20alpha-hydroxycholesterol is 17mum. 7. 25-Oxo-27-norcholesterol inhibits cholesterol oxidation non-competitively (K(i)16mum). A number of other Delta(5)-3beta-hydroxy steroids inhibit cholesterol oxidation and evidence was obtained that the 3beta-hydroxyl group was necessary for inhibitory activity. 8. Pregnenolone, 20alpha-hydroxycholesterol and 25-oxo-27-norcholesterol inhibit oxidation of cholesteryl sulphate by this system but their sulphates do not. 9. 3beta-Hydroxychol-5-enoic acid, 3alpha-hydroxy-5beta-cholanic acid and 3beta-hydroxy-22,23-bisnorchol-5-enoic acid stimulated formation of isocaproic acid from cholesterol. 10. No evidence was obtained that phosphorylation or sulphation are obligatory steps in cholesterol oxidation by adrenal-cortex mitochondria. 11. The cholesteryl 3beta-sulphate sulphatase of bovine adrenal cortex was found mostly in the microsomal fraction and was inhibited by inorganic phosphate.
Studies on the nature of microsome-bound substances involved in the biosynthesis of acidic glycoproteins of guinea-pig serum
Authors: Simkin J. L. , Jamieson J. C.
Published: August 2015

1. In further studies on the biosynthesis of components of fraction I, an acidic glycoprotein-containing fraction from guinea-pig serum, an investigation was made of the substances bound to liver microsomes that had earlier been implicated to participate in the synthesis of components of fraction I present in serum. These substances were normally liberated by ultrasonic vibrations. Antisera to subfractions of fraction I were used for characterization. 2. At pH8·6, most of the microsome-bound substances showed electrophoretic mobilities lower than components of fraction I but similar to components of sialic acid-free fraction I. 3. The sialic acid/protein ratios of immune precipitates formed by microsome extracts were similar to those of precipitates formed by sialic acid-free fraction I. 4. On chromatography on Sephadex G-150, most of the microsomal substances were eluted at an essentially similar volume to the main components of fraction I. 5. It was concluded that most of the microsome-bound substances lack sialic acid residues, and, as appreciable degradation of completed molecules is unlikely, these substances appear to be precursors of serum glycoprotein molecules with incomplete prosthetic groups. 6. Evidence was obtained on the submicrosomal localization of incomplete and complete serum glycoprotein molecules.
Comparison of some minor activities accompanying a preparation of sodium-plus-potassium ion-stimulated adenosine triphosphatase from pig brain
Authors: Fujita M. , Nagano K. , Mizuno N. , Tashima Y. , Nakao T. , Nakao M.
Published: August 2015

1. An ATPase (adenosine triphosphatase) preparation obtained from pig brain microsomes by treatment with sodium iodide showed four apparently different ouabain-sensitive activities under various conditions. They were (a) ouabain-sensitive Mg2+-stimulated ATPase, (b) K+-stimulated ATPase, (c) (Na+,K+)-stimulated ATPase and (d) Na+-stimulated ATPase activities. 2. These activities showed the same substrate specificity, ATP being preferentially hydrolysed and CTP slightly. AMP was not hydrolysed. 3. These activities were inhibited by low concentration of ouabain. The concentration producing 50% inhibition was 0·1μm for ouabain-sensitive Mg2+-stimulated ATPase, 0·2μm for K+-stimulated ATPase, 0·1μm for (Na+,K+)-stimulated ATPase and 0·003μm for Na+-stimulated ATPase activity. 4. The ouabain-sensitive ATPase activities were inactivated by N-ethylmaleimide but the insensitive ATPase activity was not. 5. The three ouabain-sensitive ATPase activities were inhibited about 50% by 1mm-Ca2+, whereas the ouabain-sensitive Mg2+-stimulated ATPase activity was activated by the same concentration of Ca2+. The preparation was treated with ultrasonics at 20kcyc./sec. The 2min. ultrasonic treatment inactivated the ATPase activities by 50%. 7. The temperature coefficient Q10 was 6·6 for K+-stimulated ATPase activity, 3·7 for (Na+,K+)-stimulated ATPase and 2·6 for Na+-stimulated ATPase. 8. Organic solvents inactivated the ATPase activities, to which treatment the K+-stimulated ATPase was the most resistant. 9. The phosphorylation of the enzyme preparation became less dependent on Na+ with decreasing pH. This Na+-independent phosphorylation at low pH was sensitive to K+ and hydroxylamine as well as the Na+-dependent phosphorylation at neutral pH.
Mechanism of choline O-sulphate utilization in fungi
Authors: Spencer B. , Hussey E. Caroline , Orsi B A , Scott J M
Published: August 2015

1. The position of the enzyme blocks in a number of parathiotrophic mutants of Aspergillus nidulans A 69 and mutants A and C of a biotinless mutant of Aspergillus nidulans were examined by nutritional and heterokaryosis experiments and by assay in vitro of enzyme systems and specific enzymes. 2. The mutants were in five groups: A and C blocked at sulphate transport; gamma at ATP sulphurylase; iota at adenosine 5′-sulphatophosphate kinase; eta at the adenosine 3′-phosphate 5′-sulphatophosphate reductase system; α, β and γ between sulphite and thiosulphate. 3. The ability of the various mutants to synthesize choline O-sulphate in vivo and in vitro and to utilize choline O-sulphate as a source of sulphur indicated that the utilization of endogenously formed choline O-sulphate involved the splitting off of inorganic sulphate, which was then reduced. 4. Choline O-sulphate acted as a source of choline for cholineless strains of Neurospora crassa, suggesting that choline O-sulphate breakdown occurred by simple hydrolysis involving a choline sulphatase. 5. After de-repression of mycelia by growing for a period on a sulphur-free medium the presence of choline sulphatase in physiologically significant amounts was demonstrated in all the A. nidulans strains tested. 6. Choline O-sulphate is transported across the mycelial wall by a mechanism different to that responsible for inorganic sulphate transport.
Isopentenyl pyrophosphate isomerase from liver
Authors: Holloway P. W. , Popják G.
Published: August 2015

Isopentenyl pyrophosphate isomerase (EC 5.3.3.2) was purified from extracts of pig liver by ammonium sulphate fractionation and by gel filtration. After about 20-fold purification the preparations were free of phosphatase and prenyltransferase (EC 2.5.1.1), the two enzymes that could have interfered with the assays. The isomerase has a distinct pH optimum at 6·0 and is activated by Mn2+ in preference to Mg2+. The Km value for isopentenyl pyrophosphate is 4×10−6m. The equilibrium of the reaction favours the formation of dimethylallyl pyrophosphate. The reversibility of the isomerase reaction was demonstrated directly by the formation of isopentenyl pyrophosphate from dimethylallyl pyrophosphate. It is suggested that two prenyl isomerases might exist, one involved in the synthesis of trans- and another in the synthesis of cis-polyprenyl substances.
Studies on the protein-bound chondroitin sulphate of bovine cortical bone
Authors: Herring G. M.
Published: August 2015

A fraction containing chondroitin sulphate, isolated from bovine cortical bone under mild conditions, was separated by ion-exchange chromatography into three fractions with apparent homogeneity on electrophoresis and ultracentrifugation. Two of these appeared to consist of chondroitin sulphate bound to a glycoprotein ‘core’ that had similarities to the bone sialoprotein described previously. The differences in composition of the two fractions were considered to be due to variation in the number or lengths of the polysaccharide chains. The presence of xylose and the alkali-lability of the bond between protein and polysaccharide suggested the presence of a xylosylserine linkage. The third fraction had the properties of a relatively pure chondroitin sulphate which contained a small amount of peptide. These fractions differed considerably from the protein–polysaccharide complexes of epiphysial and other cartilages, and their relevance to the possible role of glycosaminoglycans is discussed.
N-Acetyl-β-glucosaminidases in human spleen
Authors: Robinson D. , Stirling J L
Published: August 2015

1. The N-acetyl-β-glucosaminidase of human spleen has been separated by gel electrophoresis into two components, an acidic form A and a basic form B. 2. The two forms are readily separated on DEAE-cellulose and have been concentrated 50-fold and sevenfold respectively. 3. They show similar Km values towards 4-methylumbelliferyl N-acetyl-β-d-glucosaminide, and have the same pH optima when compared in citrate, phosphate or acetate buffers. They are inhibited to a similar extent by acetate, heparin, N-acetylgalactosaminolactone, N-acetyl-β-d-galactosamine and N-acetyl-β-d-glucosamine. Specificity for C-4 orientation is not absolute and p-nitrophenyl β-galactosaminide is also hydrolysed but at a rate only 11·6% of that for the corresponding glucosaminide. 4. N-Acetyl-β-glucosaminidase B is stable over a wider pH range than is N-acetyl-β-glucosaminidase A, and is less easily denatured by heat. 5. Tissue fractionation indicates that both the A and B forms are present in the lysosomal fraction, whereas the supernatant contains the A form only. 6. Evidence is presented to indicate that the A form contains a number of sialic acid residues.
Relaxation of catabolite repression in streptomycin-dependent Escherichia coli
Authors: Coukell M. B. , Polglase W. J.
Published: August 2015

Acetohydroxy acid synthetase, which is sensitive to catabolite repression in wild-type Escherichia coli B, was relatively resistant to this control in a streptomycin-dependent mutant. The streptomycin-dependent mutant was found to be inducible for β-galactosidase in the presence of glucose, although repression of β-galactosidase by glucose occurred under experimental conditions where growth of the streptomycin-dependent mutant was limited. Additional glucose-sensitive enzymes of wild-type E. coli B (citrate synthase, fumarase, aconitase and isocitrate dehydrogenase) were found to be insensitive to the carbon source in streptomycin-dependent mutants: these enzymes were formed by streptomycin-dependent E. coli B in equivalent quantities when either glucose or glycerol was the carbon source. Two enzymes, glucokinase and glucose 6-phosphate dehydrogenase, that are glucose-insensitive in wild-type E. coli B were formed in equivalent quantity on glucose or glycerol in both streptomycin-sensitive and streptomycin-dependent E. coli B. The results indicate a general decrease or relaxation of catabolite repression in the streptomycin-dependent mutant. The yield of streptomycin-dependent cells from glucose was one-third less than that of the streptomycin-sensitive strain. We conclude that the decreased efficiency of glucose utilization in streptomycin-dependent E. coli B is responsible for the relaxation of catabolite repression in this mutant.
The attachment of polyuridylic acid to reticulocyte ribosomes
Authors: Williamson A. R.
Published: August 2015

The attachment of polyuridylic acid to reticulocyte ribosomes was studied by using polyadenylic acid, which inhibits the attachment reaction only, while permitting translation of polyuridylic acid bound to ribosomes. After addition of polyadenylic acid the amount of polyphenylalanine synthesized under standard conditions was taken as a measure of the bound polyuridylic acid. In this way certain parameters of the attachment reaction and the subsequent translation of attached polyuridylic acid were defined: (1) polyuridylic acid–ribosome interaction at 37° requires only Mg2+ at an optimum concentration of 8mm; (2) K+ (required for translation) is a non-competitive inhibitor of the attachment reaction; (3) optimum polyphenylalanine synthesis directed by attached polyuridylic acid occurs at 5mm-Mg2+ concentration; (4) from kinetic studies single ribosomes appear to participate in the attachment reaction.
The isolation and properties of experimental allergic encephalitogenic protein
Authors: Palmer F. B. , Dawson R. M. C.
Published: August 2015

1. Experimental allergic encephalitogenic (EAE) protein was isolated from ox spinal cord by a modification of the method of Martenson & LeBaron (1966). 2. The protein was examined by acrylamide-gel electrophoresis and its amino acid composition determined. 3. Sedimentation-velocity runs in the ultracentrifuge indicate a molecular weight of about 15100 at pH7·8, and calculation suggests that approx. 137 amino acid residues are present per molecule. 4. Gel-filtration and diffusion studies suggest that the protein is non-globular. 5. Optical-rotatory-dispersion measurements show the protein to have no helical secondary structure even at pH values near to the isoelectric point. In the presence of triphosphoinositide, changes in the optical rotatory dispersion of the protein could be interpreted to mean that it develops a small degree of secondary structure. 6. On treatment with cyanogen bromide the experimental allergic encephalitogenic protein is split into at least two fragments, the larger of which is only about 12% smaller than the parent protein and is antigenically active, and the smaller of which is devoid of antigenic activity.
Influence of amino acid supply on ribosomes and protein synthesis of perfused rat liver
Authors: Jefferson L. S. , Korner A.
Published: August 2015

1. The livers of rats were perfused in situ with medium containing mixtures of amino acids in multiples of their concentration in normal rat plasma. The incorporation of labelled amino acid into protein of the liver and of the perfusing medium increased with increasing amino acid concentration. During 60min. perfusions, labelling of liver protein reached a plateau, and labelling of medium protein was inhibited when the initial concentration of the amino acid mixture was more than ten times the normal plasma value. 2. Examination of polysome profiles derived from livers perfused without amino acids in the medium showed that the number of large aggregates was decreased and the number of small aggregates, particularly monomers and dimers, was increased with time of perfusion. The addition of amino acids to the perfusion medium reversed this polysome shift to an extent that was dependent on the initial concentration of amino acids. Polysome profiles derived from livers perfused for 60min. with ten times the normal plasma concentration of amino acids were essentially the same as the polysome profiles of normal non-perfused livers. 3. The ability of ribosome preparations from perfused livers to incorporate amino acids into protein in vitro decreased with increasing time of perfusion when no amino acids were added to the medium, but increased as the concentration of amino acids in the perfusion medium was increased. 4. The ability of cell sap from perfused livers to support protein synthesis in vitro was not influenced by the amino acid concentration of the perfusion medium. 5. Livers were perfused for 60min. with medium containing amino acid mixtures at ten times the normal plasma concentration but deficient in one amino acid. Maximal incorporation of labelled amino acid into liver protein, the stability of the polysome profile and the ability of ribosome preparations to incorporate amino acids into protein were found to depend on the presence of 11 amino acids: arginine, asparagine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, threonine, tryptophan and valine. A mixture of these 11 amino acids, at ten times their normal plasma concentration, stimulated the incorporation of labelled amino acid into liver protein, stabilized the polysome profile and increased the ability of ribosome preparations to incorporate amino acids into protein to the same extent as the complete mixture. 6. It is concluded that the availability of certain amino acids plays an important role in the control of protein synthesis, possibly by stimulating the ability of ribosomes to become, and to remain, attached to messenger RNA.
Catabolite repression of the lac operon. Separate repression of two enzymes
Authors: Yudkin M D
Published: August 2015

1. Catabolite repression of β-galactosidase and of thiogalactoside transacetylase was studied in several strains of Escherichia coli K 12, in an attempt to show whether a single site within the structural genes of the lac operon co-ordinately controls translational repression for the two enzymes. In all experiments the rate of synthesis of the enzymes was compared in glycerol–minimal medium and in glucose–minimal medium. 2. In a wild-type strain, glucose repressed the synthesis of the two enzymes equally. 3. The possibility that repression was co-ordinate was investigated by studies of mutant strains that carry deletions in the genes for β-galactosidase or galactoside permease or both. In all of the strains with deletions, the repression of thiogalactoside transacetylase persisted, and it is concluded that there is no part of the structural gene for β-galactosidase that is essential for catabolite repression of thiogalactoside transacetylase. 4. Subculture of one strain through several transfers in rich medium greatly increased its susceptibility to catabolite repression by glucose. It is concluded that unknown features of the genotype can markedly affect sensitivity to catabolite repression. 5. These results make it clear that one cannot draw valid conclusions about the effect of known genotypic differences on catabolite repression from a comparison of two separate strains; to study the effect of a particular genetic change in a lac operon it is necessary to construct a partially diploid strain so that catabolite repression suffered by one lac operon can be compared with that suffered by another. 6. Four such partial diploids were constructed. In all of them catabolite repression of β-galactosidase synthesized by one operon was equal in extent to catabolite repression of thiogalactoside transacetylase synthesized by the other. 7. Taken together, these results suggest that catabolite repression of β-galactosidase and thiogalactoside transacetylase is separate but equal.
A purification and some properties of an insecticidal exotoxin from Bacillus thuringiensis Berliner
Authors: Bond R. P. M. , Boyce C. B. C. , French S. J.
Published: August 2015

An insecticidal exotoxin from Bacillus thuringiensis var. thuringiensis (Berliner) has been purified. The efficiency of each stage of the purification has been ascertained and the yield of toxic material estimated by means of a quantitative bioassay. It is shown that the exotoxin is an adenine derivative substituted at position 9 and having a molecular weight of approximately 825. It can be dephosphorylated enzymically or chemically under conditions that define the exotoxin as a phosphomonoester. This results in loss of toxicity, both to insects and to mice. Spectroscopic and kinetic data are presented which suggest that a β-ribofuranosyl moiety may be attached to the adenine. Glucose and allomucic acid have been positively identified as hydrolysis fragments from the exotoxin. These results are discussed and compared with the results of others on similar (or possibly identical) compounds.
Phosphate-stimulated breakdown of 5′-methylthioadenosine by rat ventral prostate
Authors: Pegg A E , Williams-Ashman H G
Published: August 2015

A soluble enzyme preparation catalysing the release of adenine from 5′-methylthioadenosine was purified some 30-fold from extracts of the rat ventral prostate. This reaction was completely dependent on addition of inorganic phosphate ions to the assay medium. This absolute requirement for phosphate ions suggests a phosphorolytic cleavage mechanism. After acid treatment, the other product of the reaction appeared to be 5-methylthioribose. The actions of some other well-characterized enzymes of nucleoside metabolism of 5′-methylthioadenosine were also investigated; purified purine nucleoside phosphorylases from calf spleen and human erythrocytes did not attack 5′-methylthioadenosine. The role of 5′-methylthioadenosine in mammalian tissues is discussed.
Isolation of chick intestinal nuclei. Effect of vitamin D3 on nuclear metabolism
Authors: Lawson D. E. M. , Wilson P. W. , Barker D. C. , Kodicek E.
Published: August 2015

1. Chick intestinal nuclei were isolated, with practically no contamination from other organelles and whole cells, by centrifugation through 2·4m-sucrose. 2. The proportions of RNA, DNA and protein of the isolated nuclei were unaffected by the vitamin D status of the birds. The RNA/DNA ratio was 0·15. 3. The incorporation of [5−3H]orotic acid into the rapidly labelled intestinal nuclear RNA, after a 10min. pulse of the orotic acid, was increased in vitamin D-deficient chicks only 10min. after a 125μg. dose of cholecalciferol. 4. There was no stimulation of the DNA-dependent RNA polymerase activity of the isolated nuclei from birds treated with cholecalciferol. 5. The results are discussed in relation to the changes occurring during the lag period, after administration of cholecalciferol and before Ca2+ transport is detected, and the function of the vitamin.
The effects of substrates on the optical rotatory dispersion of carnitine acetyltransferase
Authors: Tipton K F , Chase J. F. A.
Published: August 2015

1. The optical rotatory dispersion of carnitine acetyltransferase is altered in the presence of l-carnitine or acetyl-l-carnitine. These changes, which include an increase in the reduced mean residue rotation at 233nm. ([M′]233), suggest that substrate binding causes the enzyme to unfold. 2. CoA and acetyl-CoA have no immediate effect on [M′]233 and CoA has no effect on the change in this parameter induced by l-carnitine. 3. The change in [M′]233 was used as a measure of the degree of saturation of the enzyme with carnitine substrates. Dissociation constants for the enzyme complexes with l-carnitine, d-carnitine and acetyl-l-carnitine were determined in this way. 4. Prolonged incubation of carnitine acetyltransferase in the presence of CoA leads to a small increase in the value of [M′]233 accompanied by irreversible inhibition of the enzyme. 5. Optical-rotatory-dispersion studies of two specifically inhibited enzyme forms are reported.
Preparation of ribosome-free membranes from rat liver microsomes by means of lithium chloride
Authors: Scott-Burden T. , Hawtrey A. O.
Published: August 2015

1. Treatment of washed rat liver microsomes in a medium containing 0·12m-sucrose, 12·5mm-potassium chloride, 2·5mm-magnesium chloride and 25mm-tris–hydrochloric acid buffer, pH7·6, with 2m-lithium chloride at 5° for 16hr. leads to the formation of membranes free of ribosomes and ribosomal subunits. 2. Confirmation of the absence of ribosomes from lithium chloride-prepared membranes was obtained by treatment of the membranes with sodium deoxycholate, followed by sucrose-density-gradient centrifugation, which showed the complete absence of ribosomes. 3. Treatment of membranes with phenol, followed by sucrose-density-gradient analysis of the isolated RNA, showed the presence of a small amount of 4s material. Repetition of the phenol extraction procedure in the presence of liver cell sap as a ribonuclease inhibitor again showed the presence of only 4s material. The 4s RNA was shown to be transfer RNA by the fact that it had the same capacity for accepting 14C-labelled amino acids as isolated transfer RNA from rat liver pH5 enzyme. 4. Analysis showed that microsomes and membranes possessed similar glucose 6-phosphatase, NADH–2,6-dichlorophenol-indophenol reductase, NADH–neo-tetrazolium reductase, NADH–cytochrome c reductase and ribonuclease activities. 5. 3H-labelled ribosomal RNA binds to membranes. However, isolation of the bound RNA by the phenol extraction procedure, followed by sucrose-density-gradient analysis, shows the RNA to be degraded to 7s material. Very little breakdown of 3H-labelled ribosomal RNA bound to membranes occurs if the binding and isolation are carried out in the presence of liver cell sap.
Liver adenosine triphosphate content and bile flow rate in the rat
Authors: Slater T. F. , Delaney V. B.
Published: August 2015

The effects of a number of hepatotoxic and other agents on the ATP content of rat liver are described. Changes in the distribution of ATP between the cell sap and the large-particle fraction were determined at intervals after rats had been dosed with various substances. Ethionine produced a rapid decrease in total liver ATP but no alteration in its intracellular distribution. Carbon tetrachloride, sodium salicylate, dimethylnitrosamine, 2,4-dinitrophenol, icterogenin, sodium succinate, sodium malonate and sodium taurocholate did not significantly alter the total ATP content of liver in the periods studied but changes in intracellular distribution were found. Carbon tetrachloride, malonate and taurocholate decreased, and salicylate treatment increased, the proportion of ATP in the cell sap. Treatment with sodium phenobarbitone increased the total liver ATP and the total amount of ATP in the cell sap. The changes in ATP concentration and in the intracellular distribution of ATP are correlated with changes previously reported in bile flow (Delaney & Slater, 1969). No general correlation was found between changes in total ATP and changes in bile flow rate, but there was a relationship between changes in bile flow and in ATP content in the case of ethionine. With the exception of taurocholate and icterogenin, which possibly act on a membrane site, an approximate correlation was found between changes in bile flow and changes in the amount of ATP in the cell sap. The findings are discussed in terms of possible mechanisms for biliary secretion.
The metabolic heterogeneity of rabbit ear cartilage chondroitin sulphate
Authors: Bentley J. Peter , Rokosová Bohumila
Published: August 2015

The only glycosaminoglycans that can be isolated from the ear cartilage of 2-month-old rabbits are chondroitin 4-sulphate and chondroitin 6-sulphate. These chondroitin sulphates exhibit molecular-weight polydispersity when isolated from tissue by papain digestion. The chondroitin sulphate is metabolically heterogeneous in that radioactive precursors [14C]glucose or [35S]sulphate are preferentially incorporated into the higher-molecular-weight polymers both in vivo and in vitro. No transfer of radioactivity from the high-molecular-weight chondroitin sulphate to the low-molecular-weight chondroitin sulphate was seen during 15 days in vivo. It is suggested that there are at least two pools of proteoglycan in the tissue. One of these pools is metabolically active whereas the other is not.
The amino acid sequence of cysteic acid-containing peptides from performic acid-oxidized ovotransferrin
Authors: Elleman T. C. , Williams J.
Published: August 2015

1. The half-cystine content of ovotransferrin, measured as cysteic acid, was 31mol/80000g of protein. 2. The amino acid sequences of cysteic acid-containing peptides from performic acid-oxidized ovotransferrin were studied. 3. 34 unique cysteic acid residues were identified. 4. It is concluded that hen ovotransferrin does not consist of two identical halves or subunits.
The effect of pH on the characteristics of the binding of nicotinamide–adenine dinucleotide by nicotinamide–adenine dinucleotide specific isocitrate dehydrogenase from pea mitochondria
Authors: Cox G. F. , Davies D. D.
Published: August 2015

1. The effect of pH on the Vmax. and concentration of NAD+ at half-maximum velocity at a constant isocitrate concentration was examined, and the results were related to the requirements for binding of H+ ions to the enzyme. 2. The effect of varying the NAD+ concentration on the pH optimum with constant isocitrate concentration was studied. 3. A comparison has been made between the effect of isocitrate concentration on the characteristics of binding of NAD+ and the effect of NAD+ concentration on the characteristics of isocitrate binding at three different pH values. 4. The mechanistic and metabolic significance of these studies is considered.
Occurrence and properties of a thermostable protease secreted by sea-urchin embryos
Authors: Barrett Dennis
Published: August 2015

1. A trypsinogen-activating enzyme is distinct from the chorion-dissolving enzyme of the sea-urchin blastula, but is secreted with it. 2. This ‘trypsinogenase’ does not attack N-α-toluene-p-sulphonylarginine methyl ester, and is not inhibited by concentrations of di-isopropyl phosphorofluoridate or 7-amino-1-chloro-3-toluene-p-sulphonamidoheptan-2-one that are 98% effective against trypsin. It requires a small amount of Ca2+ for activity, but is inhibited by more, from as little as 1mm. 3. Enzymic activity is associated with a wide range of particle weights, some apparently as high as 15×106. The mean particle weight can be decreased by sonication. 4. Fresh trypsinogenase in the higher range of particle weights appears to be remarkably stable to heating, e.g. retaining full activity after boiling for 15min.
Phase separation in an aqueous quaternary system
Authors: Edmond Elizabeth , Ogston A. G.
Published: August 2015

(1) We have measured the incompatible phase separation that occurs in a polyethylene glycol–sodium dextran sulphate–sodium chloride–water system and have determined a critical point. (2) We have measured the activity coefficients of sodium chloride in critical-point concentrations of polyethylene glycol and sodium dextran sulphate respectively, and the osmotic coefficient of sodium dextran sulphate at the critical-point concentration. (3) With use of the relevant thermodynamic equations for a quaternary ionic system, we have determined the interaction coefficients between polyethylene glycol and dextran sulphate and between polyethylene glycol and sodium chloride. The former could be due mainly to volume exclusion, but the latter is too large to be explained on that basis.
The regulation of xanthine oxidase. Inhibition by reduced nicotinamide–adenine dinucleotide of rat liver xanthine oxidase type D and of chick liver xanthine dehydrogenase
Authors: Corte E. Della , Stirpe F.
Published: August 2015

1. Rat liver xanthine oxidase type D (NAD+-dependent) and chick liver xanthine oxidase are inhibited by NADH, which competes with NAD+. 2. The addition of a NADH-reoxidizing system in the assay of these enzyme activities is proposed. 3. Rat liver xanthine oxidase type O (oxygen-dependent) is not affected by NADH.
Histone F1. Purification and phosphorus content
Authors: Buckingham R. H. , Stocken L. A.
Published: August 2015

1. Two minor protein fractions (B and C) were separated from histone F1 by chromatography on DEAE-cellulose. Fraction B was acidic. 2. Uptake of 32P in vivo into histone F1 but not into fractions B and C was stimulated by partial hepatectomy. 3. It is suggested that partial hepatectomy causes an increase in the number of histone F1 molecules phosphorylated.
A reinvestigation of the substrate specificity of pig kidney diamine oxidase
Authors: Bardsley W. G. , Hill C. M. , Lobley R. W.
Published: August 2015

1. The substrate specificity of pig kidney diamine oxidase was reinvestigated with a purer enzyme preparation than has previously been used for this purpose. 2. All substrates were extensively purified before use, and methods of preparation or sources are given, together with RF values. 3. The substrate specificity determined differed somewhat from that reported by previous workers and, in addition, the behaviour of several compounds not previously used as substrates is described. 4. A model for enzyme–substrate interaction embodying these observations is formulated. It is suggested that a negatively charged substrate-binding group is situated at 6.0–9.0 Å from the oxidizing site. The binding and oxidizing sites are separated by a hydrophobic or methylene-binding site.
Phosphatidic acid and phosphatidylinositol metabolism in Schizosaccharomyceas pombe
Authors: White G. L. , Hawthorne J. N.
Published: August 2015

The phospholipid composition of Schizosaccharomyces pombe was not markedly affected by changes in the phosphate concentration of the medium or phase of growth. The major fatty acids in the total lipid extract and purified phosphatidylinositol were palmitic acid and oleic acid. Phosphatidic acid was synthesized by acylation of l-3-glycerophosphate in Schiz. pombe and phosphatidate phosphohydrolase was present. Phosphatidylinositol synthesis from inositol occurred in the absence of CDP-diglyceride. Even with dialysed cell-free preparations, the inositol lipid was synthesized by an apparently energy-independent route, at rates greater than would be required during cell growth. Phosphatidylinositol appeared to be broken down by a phospholipase D. All the enzymes examined were particulate; similar activities were found in Saccharomyces cerevisiae.