bluuebunny/crossref_metadata_2025_split huggingface dataset:
Étude de la dissociation, par le désoxycholate de sodium, des polyparticules ribonucléoprotéiques nucléaires du cerveau de rat
Authors: Stévenin James , Jacob Monique 
Published: March 2005

The action of sodium deoxycholate (10g/l) on nuclear particles containing DNA‐like RNA from rat brain was studied. Under our experimental conditions, the size of the RNA remained unchanged when the particles were treated with deoxycholate. Therefore, modifications of the properties of the particles cannot be attributed to the release of latent RNAases by the detergent.The density, in CsCl, of the particles increased from 1.40 to 1.46–1.64 g/ml and their sedimentation coefficient decreased 30 to 50%, depending on the conditions of treatment with deoxycholate.It was calculated that an average 65% loss of proteins (as determined by density measurements) should cause a 32% reduction in the sedimentation coefficient of 150 S particles; the observed reduction was 39%. The agreement indicates that deoxycholate did not reveal hidden breaks in RNA, but only released proteins.Native particles were converted to 40‐S monoparticles upon mild ribonuclease hydrolysis, as is already known. Their density decreased slightly (from 1.41 to 1.39 g/ml) corresponding to a 10% loss of RNA. Complexes of a density between that of particles and released proteins were never observed. Such complexes would be expected if the RNA was progressively hydrolysed without modification of the protein moiety. In contrast, when the enzymatic action was allowed to proceed, particles disappeared progressively without further change in density.The behaviour of deoxycholate‐treated particles upon ribonuclease hydrolysis was different. The enzyme transformed the treated particles of high density (1.48 g/ml) into 5–20 S ribonucleoproteins of density 1.40 g/ml. Complexes of lower density were not detected.The appearance of fragments of density similar to that of native particles during RNAase action on treated particles, as well as the absence of complexes of density lower than 1.39 g/ml during RNAase action on native particles, are in favour of the type “folded ribonucleoprotein strand” structure for the monoparticle. The experimental results are in contradiction with the informofer structure proposed by Georgiev's group. The reasons for the discrepancy are not clear.
Integrity of the DNA Template, a Prerequisite for the Faithful Transcription of Xenopus rDNA in vitro
Authors: Hecht Ralph M. , Birnstiel Max L. 
Published: March 2005

RNA polymerase from Micrococcus luteus transcribes in vitro the cistrons specifying ribosomal RNA in Xenopus laevis DNA. The rDNA template is transcribed asymmetrically in the same sense as in vivo; furthermore the rDNA spacer which is not transcribed in vivo is also poorly transcribed by the bacterial RNA polymerase. The essential conditions for such near fidelity to rDNA transcription in vivo is the use of native rDNA which exhibits a high, single‐strand molecular weight of 8–10 × 106. Regardless of the cation present during the reaction it is shown by critical hybridization and hybridization‐competition studies that 90% of the RNA synthesized on this template (cRNA) is complementary to the ribosomal cistrons. It is also shown that in short incubation the M. luteus RNA polymerase initiates RNA synthesis preferentially near the 18‐S cistron and that some of the transcribed spacer DNA coding for the RNA excess of the ribosomal 40–S precursor is located adjacent to the 18‐S cistron. In longer incubations the “intact”, large molecular weight primer allows the polymerase to read through to the 28‐S cistron while “nicked” rDNA inhibits this polymerization.Both “nicked” or “intact” native rDNA produce an asymmetric cRNA but the latter exhibits a higher degree of asymmetry and loci specificity. Denatured rDNA produces a cRNA which shows no strand specificity and no loci specificity, i.e. 50% of the cRNA is complementary to each strand of rDNA and about half its sequences are complementary to the spacer DNA. In support, the cRNA is capable of competing out all labelled 28‐S and 18‐S RNA hybridization. It is also shown that the RNA sequences complementary to spacer rDNA are unique to rDNA and are not located elsewhere in the genome of Xenopus laevis.
Spectral Studies of the Interaction of Bovine α‐Lactalbumin and Egg‐White Lysozyme with 2‐p‐Toluidinylnaphthalene‐6‐sulfonate
Authors: Barel André O. , Turneer Mireille , Dolmans Marcel 
Published: March 2005

The extrinsic fluorescence of a bound dye, 2‐p‐toluidinylnaphthalene‐6‐sulfonate was used in order to study and to compare the hydrophobic sites on the surface of bovine α‐lactalbumin and egg‐white lysozyme.
Both α‐lactalbumin and lysozyme bind one mol toluidinylnaphthalenesulfonate per mol protein, as determined fluorimetrically.
The dissociation constants of the protein · dye complex for the two proteins are similar (0.3 to 0.5 mM), indicating a moderate binding of the dye to lysozyme and α‐lactalbumin.
Considering the fluorescence of the protein · dye complex and the position of the maximum in the emission spectrum, it was found that the binding site on α‐lactalbumin was more hydrophobic than lysozyme.
Binding experiments of lysozyme with toluidinylnaphthalenesulfonate in the presence of a competitive inhibitor (N‐acetyl‐d‐glucosamine) and measurements of bacteriolytic activity in the presence of this dye, suggest that the binding site on lysozyme did not significantly overlap with the area involved in the catalytic site.
The intensity of fluorescence of the bound dye in α‐lactalbumin is diminished to a small extent by the presence of various sugars (glucose, lactose and galactose). The dissociation constant of the α‐lactalbumin · dye complex is identical in the presence or in the absence of these sugars.
Calorimetric Titration of Lysozyme
Authors: Bjurulf Carin 
Published: March 2005

A method is described for enthalpy titration of proteins, using a flow microcalorimeter in combination with a device for continuous pH measurements.The calorimetric titration of lysozyme between pH 1.5 and 12 has been carried out as well as the corresponding potentiometric titration. Enthalpy values for the titrated groups are estimated and discussed in comparison with reported data for free amino acids.
Synthesis of Lens Protein in vitro Role of Methionyl‐tRNAs in the Synthesis of Calf‐Lens α‐Crystallin
Authors: Strous Ger J. A. M. , Berns Ton J. M. , van Westernen Hanske , Bloemendal Hans 
Published: March 2005

The main polypeptide chain of the lens protein α‐crystallin (αA2) is N‐terminally acetylated and contains two methionine residues. The chain is initiated by the incorporation of a methionine residue exclusively donated by methionyl‐tRNArMet.This N‐terminal methionine is not removed during polypeptide chain synthesis. The internal methionine residue is donated exclusively by one of the methionyl‐tRNAMet species. When lens messenger RNA coding for the αrA2 chain is translated in a reticulocyte cell‐free system, the newly synthesized polypeptide chain carries an acetylated methionine in the N‐terminal position.
Pyruvate Metabolism in Mitochondria from Rat Liver
Authors: Stucki Jörg W. , Walter Paul 
Published: March 2005

Rat liver mitochondria were incubated in the presence of [2‐14C]pyruvate, HCO3−, ATP and phosphate. From the measured amounts and the specific radioactivities of the products formed, metabolic fluxes through individual enzymatic reactions of pyruvate metabolism including the citric acid cycle were calculated. These fluxes and the formation of the products were simulated with a computer‐model which involved 51 reactions and 39 metabolites.Computer‐simulations and calculations of the experimental results revealed the existence of energy‐dissipating processes. About one third of the energy‐dissipation was inhibited by atractylate. It is concluded that this atractylate‐sensitive energy dissipation was due to some extramitochondrial ATPase and to the maintenance of an asymmetric distribution of ATP and ADP across the inner membrane. The atractylate‐insensitive part of energy dissipation is probably related to state 4 respiration of isolated mitochondria.Based on the specific radioactivities of malate and citrate it was concluded that the pools of malate and oxaloacetate within the matrix cannot be fully equilibrated. It is proposed that the transport of malate out of the mitochondria restricts the passage of this metabolite through the citric acid cycle.
Study of the Position of NAD and Its Effect on the Conformation of d‐Glyceraldehyde‐3‐phosphate Dehydrogenase by Small‐Angle X‐Ray Scattering
Authors: Simon István 
Published: March 2005

The structural changes of mammalian skeletal muscle d‐glyceraldehyde‐3‐phosphate dehydrogenase induced by the binding of the coenzyme, NAD, were studied by small‐angle X‐ray scattering with the double‐monitor technique.
As shown by our difference method the radius of gyration of the apoenzyme decreases by 0.08 nm on the binding of four molecules of NAD. The decrease in the radius of gyration is not a monotonous function of saturation with NAD.
From the analysis of our data it follows that, in the order of binding, the first and third NADs are positioned at a distance of about 2 nm from the centre of gravity of the molecule, whereas the second and fourth NADs are at a distance of about 4 nm.
As indicated by the change in the radius of gyration the protomers of the tetrameric molecule are dislocated by about 0.1–0.2 nm (i.e. 1–4°) relative to each other.
La d‐altronate: NAD‐oxydoréductase d' Escherichia coli K12
Authors: Portalier Raymond C. 
Published: March 2005

Kinetic studies were carried out in order to investigate the enzymic mechanism of Escherichia coli K12 d‐altronate: NAD‐oxydoreductaso.Initial velocity patterns (reciprocal plots) of the forward and reverse reactions are intersecting, referring to a sequential mechanism. The following numerical values of the Michaelis and dissociation constants are extracted graphically from secondary plots (slopes and intercepts of the reciprocal plots versus the reciprocal concentrations of the non‐varied substrate): Kia= 5.8 μM, Ka= 85 μM and Kb= 670 μM for the forward reaction; Kia, = 156 μM, Ka= 53 μM and Kb= 75 μM for the reverse reaction.At pH 6.3, in phosphate buffer, product‐inhibition patterns of the forward reaction suggest an ordered bi‐bi mechanism for the altronate oxydoreductase with NADH as the first substrate to add to the enzyme. The only competitive inhibition observed is when NAD+ is the product inhibitor and NADH the variable substrate, all others inhibitions being non competitive.At pH 8.9, in glycylglycine buffer, product inhibition patterns of the reverse reaction also revealed an ordered bi‐bi mechanism with altronate as the first substrate to add to the enzyme. The only competitive inhibition observed is when tagaturonate is the product inhibitor and altronate the variable substrate, all others inhibitions being non competitive.Dead‐end product inhibition studies with fructuronate, mannonate and ATP, and binding studies in relation to the protection of the enzyme against thermal inactivation, are consistent with an ordered bi‐bi enzymic mechanism for the altronate oxydoreductase.The occurrence of two possible enzymic forms of the altronate oxydoreductase according to the physical properties of the reaction medium is suggested.
Arginyl‐Transfer Ribonucleic‐Acid Synthetase from Bacillus stearothermophilus
Authors: Parfaitand Raymond , Grosjean Henri 
Published: March 2005

Arginyl‐tRNA synthetase from Bacillus stearothermophilus (NCA 1518) has been purified approximately 450‐fold to 90%, homogeneity. The enzyme has a molecular weight of 78000 as estimated by disc electrophoresis in denaturing conditions (dodecylsulfate). No subunits were revealed in these conditions. The Km values for arginine, ATP and tRNA have been determined. Like the arginyl‐tRNA synthetase from other organisms, this one from B. stearothermophilus requires tRNA to catalyse an arginine‐dependent ATP/[32P]PPi exchange reaction. Periodatetreated tRNA does not induce this exchange reaction. Aminoacylation is not completely inhibited by 2 mM pyrophosphate, indicating that the exchange reaction may be explained by the reversal of the overall aminioacylation reaction.Different methods tested failed to reveal any arginyl‐adenylate intermediary. By gel filtration, however, enzyme‐bound arginine could be isolated from a system containing all the substrates of the enzyme.The binding of arginine and ATP to arginyl‐tRNA synthetase has been studied by equilibrium partition and shows that arginine is bound only after the binding of tRNA and ATP.The binding of ATP does not depend on the presence of other substrates in the reaction mixture. One binding site for arginine and one for ATP are found per molecule of active enzyme. Periodate‐oxidized tRNA and phenoxyacetylarginyl‐tRNA did not induce the binding of arginine to the enzyme. Intact tRNA from other species which could be aminoacylated by arginyl‐tRNA synthetase from B. stearothermophilus, also induced the binding of arginine to the enzyme. Nucleotides other than ATP were not effective in the binding of arginine.It is concluded that the mechanism of action of this enzyme is a concerted one, as proposed by Loftfield and Eigner, in which arginine is bound after tRNA and ATP.
Effect of Fructose and Glyceraldehyde on Ethanol Metabolism in Human Liver and in Rat Liver
Authors: Thieden Herluf I. D. , Grunnet Niels , Damgaard Stig E. , Sestoft Leif 
Published: March 2005

The basic kinetic parameters, V and Km, have been determined for liver enzymes involved in the metabolism of fructose and ethanol in rats and man. Values, previously not reported, or which deviate significantly from those reported in the literature are as follows: The maximal activity of aldehyde dehydrogenase from human liver with acetaldehyde as substrate was determined as 43 μmol × min−1× g wet wt−1. The activity of NADP‐dependent alcohol dehydrogenase with ethanol as substrate both in rat liver and in human liver was very low. The presence of glycerate kinase (12 μmol × min−1× g wet wt−1) in human liver has been established. The Km‐value of human‐liver alcohol dehydrogenase (NAD) for d‐glyceraldehyde was determined as 80–90 mM compared to 8–10 mM for the rat liver enzyme. The NADP‐dependent alcohol dehydrogenase from human liver had a Km‐value for d‐glyceraldehyde of 2.5–3.3 mM. Glycerate kinase from human and rat liver had Km‐values for d‐glyceraldehyde of 2.5–3.0 mM and 0.03 mM, respectively.In slices of human liver the increase in ethanol‐oxidation rate caused by 11 mM fructose (‘the fructose effect’) or by 2 mM d‐glyceraldehyde was 76% and 56%, respectively.In rat‐liver slices the effect of D‐glyceraldehyde upon ethanol metabolism was inhibited 100% by rotenone. In the same experiments rotenone caused a 5001, inhibition of the basic ethanol oxidation rate and of the oxygen consumption.10 mM pyruvate, in experiments with liver slices from fasted rats, caused a 90%, increase in the ethanol oxidation rate in the absence of CO2, but only a 20%, increase in the presence of CO2 CO2 in itself caused a 70%, increase in the unstimulated oxidation of ethanol.Kinetic considerations and results reported in this paper held together with results from other laboratories lead to the conclusion that the theories previously proposed for the effect of fructose, d‐glyceraldehyde or pyruvate upon ethanol metabolism are irreconcilable with the experimental results. A new hypothesis for the ‘fructose effect’ is proposed.Malate dehydrogenase, malic enzyme, pyruvate carboxylase and transfer of oxaloacetate from the mitochondrial to the extramitochondrial compartment constitute a mechanism by which transfer of hydrogen from NADH to NADP may take place, thus increasing the rate of removal of NADH from the cytoplasm.
The Modification of the Reconstituted Sarcoplasmic ATPase by Monovalent Cations
Authors: The Rudy , Hasselbach Wilhelm 
Published: March 2005

The effects of monovalent cations on the calcium‐dependent ATPase activity of lipid‐depleted and reconstituted sarcoplasmic membranes have been investigated.
The calcium‐dependent ATPase activity of sarcoplasmic membranes whose lipid components have been modified are significantly more sensitive to activating and/or inhibitory effects of monovalent cations than that of native sarcoplasmic membranes.
Activating and inhibitory effects of the applied monovalent ions depend on the concentration of ionized calcium in the medium. In dilute calcium media ([Caz+] = 0.8 μM) modified ATPase preparations are always inhibited by high concentrations (>0.2M) of monovalent salts. Conversely, in concentrated calcium media ([Ca2+] = 0.18 mM) modified ATPase preparations are in most cases activated by increasing (>0.2 M) concentrations of monovalent salts.
Activating effects of the monovalent ions decrease and specific inhibitory effects increase in the order K+, Ria+, Rb+, Cs+, Li+. This order corresponds to that found if the ions are arranged according to the increasing distance between potassium and the respective ion on the hydration enthalpy scale.
The results have been discussed in relation to a specific competition between calcium ions bound to the inhibitory side at the inner surface of the sarcoplasmic membranes and the applied monovalent ions.
The Subunit Structure of the Pyruvate‐Dehydrogenase Complex from Escherichia coli K‐12
Authors: Vogel Otto , Hoehn Barbara , Henning Ulf 
Published: March 2005

It is shown that very likely the Escherichia coli K‐12 pyruvate dehydrogenase complex is not a unique entity in that the amount of pyruvate dehydrogenase component it contains can vary. A complex can be obtained from which “excess” pyruvate dehydrogenase component is removed and this complex, called core complex, has an entirely reproducible polypeptide chain composition. The core complex has a molecular weight of 3750000 ± 200000.In the core complex the dihydrolipoamide transacetylase component can consist of a polypeptide chain with a molecular weight of 80000 or of a number of fragments of this chain. Although fragmentation of the transacetylase need not influence the catalytic activity of the core complex it is operationally defined as that multienzyme complex which contains the transacetylase subunit with Mr= 80000.
Triiodothyronine Action on RNA Synthesis in Rat‐Liver Mitochondria
Authors: Gadaleta Maria N. , Barletta Antonio , Caldarazzo Maria , de Leo Teodoro , Saccone Cecilia 
Published: March 2005

Chronic treatment of thyroidectomized rats with physiological doses of triiodothyronine leads to a significant increase in the incorporation of [3H]UTP into RNA by isolated rat liver mitochondria after the 4th day of treatment.
The increased activity of mitochondrial RNA polymerase is followed by a net increase in the RNA content of organelles which can be observed after the 5th day of chronic treatment.
Single injection of triiodothyronine at a dose of 250 μg/kg body wt also causes great stimulation of mitochondrial RNA synthesis which increases three‐fold after 40 h.
At the same DNA/RNA ratio, RNA labelled in vitro with [3H]UTP from liver mitochondria of thyroidectomized animals hybridizes with mitochondrial DNA less efficiently than the newly synthesized RNA from liver mitochondria of animals treated for 10 days with 5 μg/100 g body wt of the hormone.
Hybridization‐competition experiments with unlabelled RNA extracted from mitochondria of treated and untreated animals seem to suggest that a change in the transcription of mitochondrial DNA under the influence of the hormone occurs also in vivo.
Characterization of the Native and Denatured Conformations of tRNASerand tRNAPhefrom Yeast
Authors: Streeck Rolf E. , Zachau Hans G. 
Published: March 2005

Previous work on the partial digestion of the native and denatured forms of tRNASerand tRNAPhefrom yeast with T1‐RNAase was extended. Detailed studies with pancreatic and T2‐RNAase and a few experiments with sheep kidney nuclease and acid RNAase from hog spleen revealed characteristically different fragmentation patterns for the native and denatured forms of the tRNAs. Apparently it is mainly the miniloop and dihydrouridine regions which are involved in the conformational changes responsible for denaturation.The rate constants, activation enthalpies, and activation entropies of the renaturation process were calculated from amino acid acceptance data.When the changes in hyperchromicity at 260 nm of the denatured tRNAs were followed as a function of time, a process was detected which in tRNAPheis 5–10 times and in tRNAser10–20 times faster than the renaturation as measured by acceptor activity. The whole net change in absorption, possibly representing the total net change in base stacking, occurs during the fast, process. The activation enthalpies and activation entropies are different for the fast and the over‐all processes.
Properties and Immunochemical Reactivities of Native and Modified Human‐Serum Albumin
Authors: Jacobsen Christian , Funding Lars , Møller Niels Peter H. , Steensgaard Jens 
Published: March 2005

A series of chemically modified derivatives of human‐serum albumin has been produced in soluble monomeric form by modification of lysine, tryptophan, tyrosine, histidine, and acidic amino‐acid residues. Optical rotatory dispersion studies suggest that human‐serum albumin has a secondary structure which is resistant to many chemical side‐chain modifications. Sephadex‐gel‐filtration data and analytical ultracentrifugations indicate that the tertiary structure of human‐serum albumin is less resistant to chemical modification than the secondary structure. The combined data suggest that the secondary and tertiary structures to some extent are mutually independent. Lysine residues are found to be of major importance in the maintenance of the native tertiary structure.Chemically modified derivatives of human serum albumin are found to have decreased abilities to combine with the corresponding rabbit antibodies by a modified Farr technique. By immunoelectrophoresis and immunodiffusion a 96% acetylation was required to destroy complete immunogenic determinants. Lysine residues were found to be of major importance to the immunochemical reactivity of human‐serum albumin, while tryptophan, acidic amino acids and tyrosine residues play a minor role. Histidine residues seem to be unimportant to the immunochemical reactivity,Comparisons between immunochemical reactivities and structural parameters of native and modified albumins showed in particular a distinct relationship between the immunochemical reactivities and the Stokes‐radius values as determined by Sephadex‐gel filtration.
Inhibition of the Assembly of Cytochrome Oxidase in Neurospora crassa by Chloramphenicol
Authors: Sebald Walter , Weiss Hanns , Jackl Gerhard 
Published: March 2005

Cytochrome oxidase was prepared from Neurospora crassa by chromatography on oleyl poly‐methacrylic acid resin and separated into seven polypeptides by polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate. Incorporation of labelled amino acids into the single polypeptides was investigated after a pulse labelling in the absence and presence of chloramphenicol, and after washing out the inhibitor.Chloramphenicol (4 mg/ml) inhibited amino acid incorporation into all polypeptides 90–95% while labelling of the whole membrane protein was inhibited only 30%. After washing out the inhibitor and further growth of the cells, the four smaller polypeptides were highly labelled, whereas the other polypeptides showed only a small increase in radioactivity. It is concluded that the four small‐sized polypeptides of cytochrome oxidase are synthesized but not integrated into the functional enzyme under the action of chloramphenicol.