bluuebunny/crossref_metadata_2025_split huggingface dataset:
Gluconeogenesis from Serine by the Serine‐Dehydratase‐Dependent Pathway in Rat Liver
Authors: Sandoval Ignacio V. , Sols Alberto 
Published: March 2005

Isolated perfused livers from rats made deficient in pyruvate carboxylase by feeding an avidin‐rich, biotin‐deficient diet produced much less glucose than those from the corresponding normal animals (0.23 ± 0.08 and 0.83 ± 0.05 μmol/g liver per min, respectively). The ability to form glucose from alanine was also markedly impaired, while that from fructose was not similarly affected. Parenteral administration of biotin led within 3 h to full recovery of the activity of hepatic pyruvate carboxylase, as well as to restoration of the ability to form glucose from serine, both by the isolated liver and by the whole animal (measured in the latter case by the formation of [14C]glucose from [14C]serine).In the perfused liver, gluconeogenesis from hydroxypyruvate and glycerate, the specific intermediates of the potential alternative pathway from serine to glucose mediated by serine pyruvate transaminase, was smaller than that from serine.The serine dehydratase in the liver of fasted rats is in terms of V (2.3 ± 0.7 U/g) and Km (approx. 40 mM) quantitatively suited to account for the rate of gluconeogenesis from serine in the perfused liver, both when offered as the only precursor at high concentration and when offered as part of a mixture of precursors at physiological concentrations. In contrast, the efficiency of the so‐called serine pyruvate transaminase to act on serine in physiological conditions appears to be utterly insufficient to permit a major contribution to gluconeogenesis from serine by this means.These results indicate that gluconeogenesis from serine in rat liver proceeds essentially by the serine‐dehydratase‐mediated pathway.
Selective Carbethoxylation of the Histidine Residues of Actin by Diethylpyrocarbonate
Authors: Hegyi György , Premecz György , Sain Béla , Mühlrád András 
Published: March 2005

Histidine residues of actin were carbethoxylated with diethylpyrocarbonate. Four and three histidine residues per actin monomer were rapidly carbethoxylated in the G and F form, respectively. After partial Carbethoxylation of G‐actin a non‐polymerizable fraction could be separated by ultracentrifugation. The analysis of these fractions showed that one of the four fast‐reacting histidines of G‐actin plays an essential role in polymerization.Removal of the carbethoxy groups from the histidine residues by hydroxylamine treatment restored the ability to polymerize.The specificity of the reaction was tested by the use of [14C]diethylpyrocarbonate.After tryptic digestion of non‐polymerizable carbethoxylated actin a single histidyl peptide was isolated by gel filtration and diagonal electrophoresis. The histidine residue essential for polymerization was identified as histidine‐40.
Distribution and Some Properties of Acid Phosphatase in the 7,12‐Dimethylbenz[a]anthraccne‐Induced Rat‐Mammary Carcinoma
Authors: Nicholson Robert I. , Davies Malcolm 
Published: March 2005

Differential centrifugation and gel‐chromatography techniques have been employed to study the distribution and molecular forms of acid phosphatase in rat mammary tumours induced by 7,12‐dimethylbenz[a]anthracene. With p‐nitrophenylphosphate as substrate three distinct forms of acid phosphatase activity were separated on gel chromatography.Enzyme I (Mr > 200000) and enzyme II (Mr 120000) were found to have similar biochemical properties and differential centrifugation indicated that both enzymes are present in a sedimentable fraction. Disruption of a mitochondrial‐lysosomal fraction by freezing and thawing released 45% of the total acid phosphatase of the fraction into a soluble phase. Treatment with detergent solubilized the bound enzyme. The possibility of two forms of acid phosphatase, one bound and one freely soluble, in the lysosomes of the rat mammary tumour is discussed.Enzyme III (Mr 30000) is localized in the soluble fraction of the tumour cell and is biochemically distinct from enzymes I and II.The overall findings are examined in relation to the properties and distribution of acid phosphatase in other tissues.
Repeated Nucleotide Sequences in the Loach Genome
Authors: Kupeijanova Natalia S. , Timofeeva Margarita Ja. 
Published: March 2005

Reassociation kinetics of loach DNA has been studied.It has been shown that 50% of the loach genome consists of repeated nucleotide sequences. Most of them belong to an “intermediate” repetitive fraction of DNA, repetition frequency being equal to 104−102.Close study of the intermediate repetitive fraction of DNA reassociation kinetics reveals the existence of discrete repetitive DNA groups in the loach genome. The DNA fractions corresponding to discrete repetitive groups were isolated and their reassociation kinetics, nucleotide composition and thermal stability were studied. The differences established allow us to postulate that DNA sequences of different repetitive groups perform distinct functions. Further investigations are to be undertaken to examine this assumption and clarify the role of each repetitive group in the genome.
Acid Denaturation of Human Carbonic Anhydrase B
Authors: Flanagan Michael T. , Hesketh T. Robin 
Published: March 2005

The acid denaturation of human carbonic anhydrase B has been followed using fluorescence spectroscopy. On lowering the pH of the protein solution through the acid unfolding transition region the quantum yield was increased and the wavelength of maximum fluorescence emission red shifted.
The rate of unfolding of the protein, as measured fluorimetrically, was shown to obey first‐order kinetics. Arrhenius plots at two ionic strengths were linear between 7 °C and 35 °C. In the pH range 3.0 to 3.8 the rate constant was second order with respect to hydrogen ion concentration. Approximately 30% of the free energy of activation for unfolding was shown to be an electrostatic contribution.
Circular diehroism spectra showed that the first, reversible unfolding step is followed by a slower irreversible step, the rate of which is reduced by the presence of Zn2+.
The irreversibly unfolded protein aggregated on increasing the pH, the onset of aggregation occurring sharply at pH 3.6.
Antigenicity of p‐Azobenzenearsonate‐Containing Oligopeptides in Rabbits
Authors: Levin Howard , Becker Martin , Sela Michael 
Published: March 2005

The denned compounds containing p‐azobenzenearsonate (Aba), Aba‐Tyr, Aba‐Tyr‐Tyr, Aba‐Tyr‐(Tyr)2, Aba‐Tyr‐(Tyr)3, (Tyr)3‐Aba‐Tyr and Aba‐Tyr‐(Ala)3 (where Tyr is l‐tyrosine and Ala is l‐alanine) were synthesized and were investigated immunologically in New Zealand white rabbits. After immunization with the peptides in complete Freund's adjuvant the antibody responses were monitored by both a hapten‐modified bacteriophage inactivation assay and quantitative antibody precipitation. The anti‐Aba antibody response was shown to increase as tyrosine residues were added to the Aba‐Tyr moiety, with the most significant jump in titer occurring between Aba‐Tyr‐Tyr and Aba‐Tyr‐(Tyr)2. In contradistinction, no increase in immunogenicity was observed when three alanyl residues were used to lengthen the peptide chain.Studies of the specificity of the anti‐Aba antibodies produced against the peptides, using inhibition of the hapten‐modified phage inactivation, indicated that, while the specificity of antibodies is direct mainly to the Aba‐Tyr moiety in these compounds, the antibodies did demonstrate specificity for the homologous immunizing antigen.The data suggests that the area adjacent to the Aba‐Tyr group on these small immunogens is important for its recognition as an immunogen and also for its ability to determine the specificity of the antibody induced.
Two Isoenzymes of Glucosephosphate Isomerase from Spinach Leaves and Their Intracellular Compartmentation
Authors: Schnarrenberger Claus , Oeser Angelika 
Published: March 2005

From spinach leaves (Spinacea oleracea L.) two isoenzymes of glucosephosphate isomerase can be separated by DEAE‐cellulose ion‐exchange chromatography. Isoenzyme 1 eluting at high ionic strength shows a faster mobility during disc gel electrophoresis than isoenzyme 2 eluting at low ionic strength. For both isoenzymes the pH‐optima and Km‐values were very similar for either direction. However, the Km‐values with glucose‐6‐phosphate as substrate (Km= 8.0 mM and 5.9 mM for isoenzyme 1 and 2, respectively) were 20‐fold higher than with fructose‐6‐phosphate as substrate (Km= 300 μM for both isoenzymes). The molecular weight of both isoenzymes was estimated by sedimentation velocity centrifugation analysis to be 120000. The subcellular distribution reveals that isoenzyme 1 is located within the chloroplasts and isoenzyme 2 in the non‐particulate cell fraction (cytosol).The results give further support to the view that in plants there exist two sets of isoenzymes for the oxidative pentose phosphate cycle, one set located in the chloroplasts, the other one in the non‐particulate cell fraction (cytosol).
On the Translational Control of Histone Synthesis
Authors: Breindl Michael , Gallwitz Dieter 
Published: March 2005

Histone mRNA was isolated from polyribosomes and other cell fractions of synchronized HeLa cells and quantitated by its translational capacity in a rabbit reticulocyte lysate. Inhibition of DNA synthesis with hydroxyurea (5 mM) results within 30 to 60 min in a loss of 80–85% of biologically active histone mRNA from polyribosomes. In contrast, actinomycin D (5 μg/ml) during the first hour of its action, only stops further accumulation of histone mRNA on polyribosomes in early S‐phase cells. Under conditions of interruption of DNA replication biologically active histone mRNA does not appear in other cell fractions suggesting that it is immediately destroyed in the cytoplasm.The possible translational control of histone synthesis in HeLa cells was investigated with special consideration of the existence of messenger‐specific initiation factors. Cell‐free extracts from synchronized HeLa cells in which DNA and histone synthesis were inhibited with hydroxyurea, fully retain their capacity to translate added homologous histone mRNA as compared with extracts from synchronized S‐phase cells. Using a partially purified protein‐synthesizing system from rat liver supplemented with initiation factors from synchronized HeLa cells differing in their histone‐synthesizing capacity, it was shown that factors from hydroxyurea‐treated cells are as active in stimulating the translation of histone mRNA, globin mRNA and tobacco mosaic virus RNA as are initiation factors from S‐phase cells. The results suggest that messenger discriminating translation factors are not involved in the regulation of histone synthesis in HeLa cells or they are very labile and inactivated during preparation.
Mode of Degradation of Ribosomes in Regenerating Rat Liver in vivo
Authors: Tsurugi Kunio , Morita Tomi , Ogata Kikuo 
Published: March 2005

The degradations of structural proteins and RNAs of ribosomes in regenerating rat liver were investigated with the following results.

Using a modification of the double isotope technique of Arias et al. (1969), it was found that almost all the structural proteins of both large and small ribosomal subunits, separated by dodecylsulfate or two‐dimensional polyacrylamide gel electrophoresis, were apparently degraded at the same rates.
Studies on the changes in the specific activities of the RNA and protein moieties of the two ribosomal subunits after administration of [Me‐3H]methionine as a common precursor showed that their specific activities decreased in parallel, with the same apparent half‐life of about 4.5 days.
These results suggest that structural components of rat liver ribosomal subunits are degraded as a unit.
Ligand‐Specific Bohr Effect in Haemoglobins
Authors: Sick Hinrich , Gersonde Klaus 
Published: March 2005

The CO binding properties of monomerie (Hb III and IV), dimeric, and tetrameric Chironomus haemoglobins as well as of the monomer‐analogue valence hybrid (αMmet2βmetβdeoxy) of Hb M Iwate were studied and compared with the respective O2 binding properties. All these haemoglobins show hyperbolic O2 binding curves and a Bohr effect. The amplitudes of the O2 Bohr effect curves range from Δlog (PO2(1/2), = 0.3 (Hb III) to 2.4 (tetrameric Chironomus haemoglobin).The ligands CO and O2 differ not only in affinity but also with regard to the Bohr effect. The CO affinities of the various Chironomus haemoglobins are 60 to 490 times larger than the O2 affinities and the amplitudes of the CO Bohr effect curves are 1.25 to 8 times smaller than those of the respective O2 Bohr effect curves. In the case of Hb M Iwate, however, the CO Bohr effect is larger than the O2 Bohr effect by the factor 1.25 (2,3‐bisphosphoglycerate‐reacted Hb M) and 1.4 (stripped Hb M).The ligand‐specific differences in the magnitude of the Bohr effect cannot be explained solely by the allosteric interaction connected with the trans‐effect of the complex. The differences are discussed in terms of steric influences on the binding geometry of the 6th ligand by protein side chains at the distal side of the haem group.
A Film Detection Method for Tritium‐Labelled Proteins and Nucleic Acids in Polyacrylamide Gels
Authors: BONNER William M. , LASKEY Ronald A. 
Published: March 2005

A simple method is described for detecting 3H in polyacrylamide gels by scintillation autography (fluorography) using X‐ray film. The gel is dehydrated in dimethyl sulphoxide, soaked in a solution of 2,5‐diphenyloxazole (PPO) in dimethylsulphoxide, dried and exposed to RP Royal “X‐Omat” film at ‐70 °C. Optimal conditions for each step are described. β‐particles from 3H interact with the 2,5‐diphenyloxazole emitting light which causes local blackening of an X‐ray film. The image produced resembles that obtained by conventional autoradiography of isotopes with higher emission energies such as 14C. 3000 dis. 3H/min in a band in a gel can be detected in a 24‐h exposure. Similarly 500 dis./min can be detected in one week.When applied to the detection of 35S and 14C in polyacrylamide gels, this method is ten times more sensitive than conventional autoradiography. 130 dis. 35S or 14C/min in a band in a gel can be detected in 24 h.
Antibodies to Chick‐Tendon Procollagen
Authors: DEHM Peter , OLSEN Bjørn R. , PROCKOP Darwin J. 
Published: March 2005

Antisera were prepared by immunizing a rabbit with procollagen synthesized and secreted by cells from chick embryo tendons. Specific antibodies were then purified from the antisera by using an immunoadsorbent which contained the isolated NH2‐terminal extensions of procollagen. The purified antibodies were shown to react specifically with intact procollagen as well as with procollagen in which the interchain disulfide bonds were ruptured by reduction under non‐denaturing conditions. The antibodies also reacted with the pro‐α1 chain but not the pro‐α2 chain isolated from the procollagen. There was no reaction after the intrachain bonds in the pro‐α chains of the procollagen were reduced under denaturing conditions and alkylated.In the course of characterizing the antibodies it was shown that the NH2‐terminal extensions on the two pro‐α1 chains and the one pro‐α2 chain of type I procollagen are non‐identical. Also, it was shown that the serum of chick embryos contains an antigen which reacts with the specific antibodies to procollagen.
Studies on Energy‐Linked Reactions: Modified Mitochondrial ATPase of Oligomycin‐Resistant Mutants of Saccharomyces cerevisiae
Authors: GRIFFITHS David E. , HOUGHTON Raymond L. 
Published: March 2005

Oligomycin resistance is expressed at the mitochondrial and submitochondrial levels in oligomycin‐resistant mutants of Saccharomyces cerevisiae. Studies of the mitochondrial ATPase and Pi‐ATP exchange reaction indicate that a modification of the mitochondrial ATPase (ATP‐synthetase) complex is involved. The specific resistance at the mitochondrial level to oligomycin and related inhibitors such as ossamycin, rutamycin and peliomycin and the lack of resistance to other inhibitors of mitochondrial ATP synthetase (triethyltin sulphate, venturicidin, aurovertin, Dio‐9) correlate with whole cell studies and provide further evidence for a specific modification of an inhibitor site on the mitochondrial inner membrane.Mitochondrial mutants which map at the OLI and OLII loci can be differentiated biochemically by their sensitivity to oligomycin of mitochondrial ATPase and the pH 9.5/pH 6.5 ATPase activity ratios.Studies utilising F1‐ATPase from wild type and oligomycin‐resistant mutants indicate that oligomycin resistance is due to a modification of a membrane‐bound component of the mitochondrial ATP‐synthetase complex and not to a modification of F1‐ATPase or the oligomycin‐sensitivity‐conferring protein.Partially purified oligomycin‐sensitive ATPase preparations (Triton X‐100 extracts) retain the sensitivity (resistance) and specificity of the original membrane‐bound system in mitochondria. Purified oligomycin‐sensitive ATPase preparations also retain the specificity of the original membrane preparation but the sensitivity to inhibitors is partially modified. The results support the conclusion that oligomycin resistance is due to modification of mitochondrially coded and mitochondrially synthesised subunits of the oligomycin‐sensitive ATPase (ATP synthetase) complex. There is no correlation of oligomycin resistance with the ergosterol concentration of yeast cells, yeast mitochondria or mitochondrial ATPase.
Bacteriophage‐Induced Ribonucleotide Reductase Systems
Authors: ERIKSSON Staffan , BERGLUND Ove 
Published: March 2005

Infection of Escherichia coli with bacteriophage T5 caused a more than 20‐fold increase in ribonucleotide reductase activity in crude cell extracts. The phage induced the formation of a new ribonucleotide reductase and a new thioredoxin.The T5‐specific ribonucleotide reductase was defined by its ability to accept the T5‐induced thioredoxin as hydrogen donor. However, the enzyme could also accept E. coli thioredoxin as hydrogen donor and it was inhibited by antisera against subunit B2 of E. coli ribonucleotide reductase. The crude phage enzyme preparation studied preferred CTP to CDP and CMP as substrate and required magnesium and ATP for activity. Its behaviour towards allosteric effectors was different from that of the host enzyme.T5‐induced thioredoxin chromatographed together with E. coli thioredoxin on DEAE‐cellulose but could be separated from the latter by immunoadsorbent chromatography. T5 thioredoxin was reduced by E. coli thioredoxin reductase but could not serve as hydrogen donor of E. coli ribonucleotide reductase.Bacteriophage T6 induced a new ribonucleotide reductase and a new thioredoxin upon infection. The T6‐induced proteins cross‐reacted functionally and immunologically with the corresponding T4‐induced proteins.Infection of E. coli B with phage T7 or induction of the lysogens E. coli K‐39 (λ+) and E. coli W‐3350 (λc1857) caused no increase in reductase activity and chromatography of cell extracts gave no evidence for the presence of new thioredoxins.
A Three‐Dimensional Atomic Model of the Murein Layer of Bacteria
Authors: FORMANEK Helmut , FORMANEK Sibylle , WAWRA Heinz 
Published: March 2005

X‐Ray diffraction, infrared spectra and density of murein, the rigid component of almost all bacterial cell walls, were measured using gram‐negative (Spirillum serpens) and gram‐positive (Lactobacillus plantarum) strains.X‐Ray diffraction of dried foils of murein showed Debye‐Scherrer rings, indicating periodicities of 0.93 to 1.00 and 0.44 nm. The comparison of the infrared spectra of chitin and murein showed that their amide I and amide II bands have the same frequencies. With isopycnic density‐gradient centrifugation of murein a density of ϱ= 1.46 g × cm−3 was observed.Based on these data, on theoretical considerations and on model building the following structure of murein is proposed: the structure of the glycan chains in murein is similar to that of chitin and cellulose. The peptides consisting of alternating d‐ and l‐amino acids have the 2.27 helical conformation. They are linked to the carbohydrate chains through their N‐terminus and form two hydrogen bonds with the sugar residues. This linkage causes an angle of about 150° between the carbohydrate and peptide chains.
γ‐Cystathionase of Rat Liver
Authors: BROWN Fountaine C. , DEFOOR Marie C. 
Published: March 2005

1. With 5′,5‐dithiobis(2‐nitrobenzoic‐acid), 8 of the 12–SH groups in native γ‐cystathionase react reversibly, but 4 form stable bonds and the inhibited product (I) can be isolated. The presence of homoserine, one of the substrates, does not affect the formation of I.2. Cystathionine, at high concentrations, partially relieves the inhibition; at low concentrations, a different inhibited product, or products, (II) is formed. In form I but not II, the enzyme is protected from reduction by borohydride.3. Dithiothreitol decomposes both I and II and 65 to 85% of the original enzyme activity can be recovered. Dithiol releases the anion, 2‐nitro‐5‐thiobenzoate, from I but not from 11.
The Influence of Methylene Blue on the Respiratory Metabolism of the Reticulocyte
Authors: RAPOPORT Samuel M. , MÜLLER Marianne 
Published: March 2005

Methylene blue selectively increases cytosolic oxidations of the rabbit reticulocytes without uncoupling mitochondrial oxidation. The endogenous substrate of methylene‐blue‐catalyzed oxygen consumption is primarily ribose phosphate, which arises from the breakdown of ribonucleic acids and free nucleotides.In the presence of methylene blue glucose is oxidized to 95%via the oxidative pentose phosphate pathway. The primary reduction product of the oxygen is H2O2, which is removed both by catalase and by the interplay of glutathione peroxidase and glutathione reductase. Thus a respiratory quotient of 1 results as determined by the balance of 14CO2 formation and O2, consumption.
Enzymatic Deacylation of Methionyl‐tRNAfMef Catalysed by Methionyl, Isoleucyl and Phenylalanyl‐tRNA Synthetases
Authors: SOURGOUTCHOV Andrei , BLANQUET Sylvain , FAYAT Guy , WALLER Jean‐Pierre 
Published: March 2005

Native and trypsin‐modified methionyl, isoleucyl and phenylalanyl‐tRNA synthetases from Escherichia coli catalyze the deacylation of methionyl‐tRNAtMet. This activity, which is pH dependent, requires the presence of MgCl2 or spermidine which are known to structure the aminoacyl‐tRNA. Investigation of the effects of cognate amino acids on the rate of enzymatic deacylation of methionyl‐tRNAtMet, reveals strikingly different behaviours of native and trypsin‐modified methionyl‐tRNA synthetases.Kinetic parameters for the deacylation of methionyl‐tRNAtmet catalyzed by native methionyl and isoleucyl‐tRNA synthetases are compared in the presence of MgCl2 and provide identical Km values of 0.2 μM while their V values, are 0.05 and 0.02 s−1, respectively. This indicates similar enzymatic efficiencies per active site and emphasizes the lack of specificity of the reaction.