bluuebunny/crossref_metadata_2025_split huggingface dataset:
The Binding of Peptidyl‐tRNA and Acylaminoacyl‐tRNA to E. coli Ribosomes
Authors: de Groot N. , Fry‐Shafrir I. , Lapidot Y. 
Published: March 2005

The non‐enzymatic binding of aminoacyl‐tRNA, N‐blocked aminoacyl‐tRNA, peptidyl‐tRNA and N‐blocked peptidyl‐tRNA to E. coli ribosomes was measured at 0.01 M magnesium ion concentration in the presence of poly U. It was found that the maximal amounts of phenylalanyl‐tRNA and peptidyl‐tRNA, that can be bound to the ribosomes are the same, but the amounts of N‐blocked phenylalanyl‐tRNA and N‐blocked peptidyl‐tRNA, that can maximally be bound to the ribosomes are much less.Phenylalanyl‐tRNA and peptidyl‐tRNA can be bound to ribosomes which are saturated in respect to N‐blocked phenylalanyl‐tRNA or N‐blocked peptidyl‐tRNA; however, the presence of the N‐blocked substrates on the ribosomes partially inhibits the additional binding of phenylalanyl‐tRNA or peptidyl‐tRNA. Aminoacyl‐tRNA added to ribosomes saturated with respect to peptidyl‐tRNA, partially displaces the peptidyl‐tRNA from its ribosomal binding site. Under the same conditions, peptidyl‐tRNA exchanges with prebound aminoacyl‐tRNA considerably less.
Structure et activité de la polynucléotide phosphorylase d'Escherichia coli: une espèce à faible poids moléculaire
Authors: Thang M. N. , Thang D. C. , Grunberg‐Manago M. 
Published: March 2005

A polynucleotide phosphorylase with a molecular weight of 100,000 has been isolated from Escherichia coli Q13 mutant and partially purified. This mutant is particularly rich in this low molecular species which can, however, also be found in small proportion in wild strains of E. coli B and K12.Low molecular weight polynucleotide phosphorylase catalyzes only one of the reactions catalyzed by native polynucleotide phosphorylase (molecular weight 200,000), i. e. the phosphoro‐lysis of polyribonucleotides, and is unable to polymerize nucleoside diphosphates. However, in so far as the phosphorolysis reaction is concerned, there are some marked differences between the 100,000 polynucleotide phosphorylase and the 200,000 enzyme isolated from wild strains: reaction only with short chains polymers, higher requirement for Mg++ ions, non‐lineartity of the reaction as a function of protein concentration.The Q13 mutant also contains a polynucleotide phosphorylase with a molecular weight of 200,000 but this enzyme is markedly different from the enzyme isolated from wild strains: in particular, it requires Mn++ for the polymerization reaction and has a higher Km for poly A in the phosphorolysis; for this latter reaction Mg++ and not Mn++ is required.The oligomeric structure of polynucleotide phosphorylase and the relation between structure and activities is discussed.
Visualisation in the Electron Microscope and Size of RNA from Animal Cells
Authors: Granboulan N. , Scherrer K. 
Published: March 2005

Ribosomal, preribosomal (pre‐rRNA) and messenger like (mlRNA) RNA molecules from animal cells have been spread in extended form for visualisation in the electron microscope, in order to measure their length. It is shown that the giant nascent pre‐rRNA and mlRNA consists of linear molecules of homogeneous shape. Their length ranges up to 3.5 μ in the case of pre‐rRNA and up to 8.5 μ for mlRNA. The correlation of apparent lengths and molecular weight of RNA is discussed. A spacing of 2.45 Å, based on the length and the chemically determined molecular weight of E. coli rRNA, allows one to assign molecular weights to rRNA and pre‐rRNA that are in fairly good agreement with published data based on sedimentation analysis. However, the 28 S rRNA has twice the length of the 18 S species, which is in disagreement with the mass relation of 2.5–3.0 observed by sedimentation. In the case of mlRNA the spacing of 3.17 Å, derived from the length to molecular weight relation of R 17 phage RNA, is more likely to give correct values than that based on rRNA. This conclusion derives from a discussion of the relation of length and molecular weights in various viral RNA molecules in a range of up to 107 daltons.Two general conclusions may be drawn from the work presented:

The high sedimentation rate of pre‐rRNA and mlRNA is not based on artificial agglomeration or particular configuration but on the real mass of molecules which contain, in the case of mlRNA, up to 30,000 bases (molecules of up to 50,000 bases are likely to exist also) in covalent linkage.
The electron microscope may be used to determine molecular weights. The precision of the values obtained may be equal to or better than those determined by sedimentation if correct spacing data are available from reference molecules of the same RNA class.
The Mechanism of Formation of Polyunsaturated Fatty Acids by Photosynthetic Tissue
Authors: Gurr M. I. , Robinson M. P. , James A. T. 
Published: March 2005

Labelled oleic acid, which is used as a substrate in studying the conversion of oleate into linoleate by Chlorella chloroplasts, is rapidly incorporated into the phospholipids. The phosphatidyl choline fraction accounts for almost all of the phospholipid label. Desaturation to linoleate lags behind the incorporation into lipids, but the newly synthesized linoleate remains esterified to phosphatidyl choline.[1‐14C]Oleoyl‐phosphatidyl choline, incubated with chloroplasts, is converted into [1‐14C]‐linoleoyl‐phosphatidyl choline, but considerable difficulties arise in presenting the lipid to the enzyme in an acceptable form. Oleoyl‐phosphatidyl choline formed in situ, however, does not present these difficulties and is desaturated at a faster rate than the CoA derivative under conditions in which unesterified fatty acid cannot be “activated”, and hence cannot be desaturated. We conclude that the precursor fatty acid can be transferred directly from the lipid to the desaturase enzyme and the product immediately accepted by a lipid to form a “desaturation‐acylation” cycle. Our data neither prove, nor exclude the possibility that the fatty acid is transformed while still attached to the lipid in ester linkage.
Lichtinduzierte, reversible Aktivitätssteigerung der NADP‐abhängigen Glycerinaldehyd‐3‐phosphat‐Dehydrogenase in Chloroplasten
Authors: Müller B. , Ziegler I. , Ziegler H. 
Published: March 2005

Irradiation of fully developed green leaves as well as irradiation of isolated chloroplasts causes a rapid, reversible increase in the activity of NADP‐linked phosphoglyceraldehyde dehydrogenase. This increase is closely connected with the functioning of the non‐cyclic electron flow of photosynthesis. It is accompanied by a decrease in the activity of the NAD‐linked enzyme.
The experiments presented here show that it is not the kinase but the dehydrogenase which is the rate limiting factor in the over‐all reaction measured up to date.
The activation of the “dark‐enzyme” (= basic enzyme) resulting in the “light‐enzyme” (= activated enzyme) is not due to an unspecific reduction of S‐S‐groups in the reactive center. Dithiothreitol only restores the activity lost during the isolation procedure of the chloroplasts.
NADPH rather than dithiothreitol causes a specific activation of the basic enzyme. However the basic enzyme must be present in the completely reduced form to undergo maximal activation. Incubation with dithiothreitol and NADPH thus results in an activation rate as high as that caused by light in vivo.
Activation of the NADP‐linked dehydrogenase could also be attained by NADPH after its partial purification by ammonium sulfate fractionation.
The activation rate by incubation with different concentrations of NADPH shows a sigmoidal type of curve.
There are characteristic differences in sensitivity between the activity of the basic enzyme and its ability to be activated at different temperatures between 52°–60°.
The results indicate that the action of NADPH may be an allosteric one, causing a transition from a NAD‐ (or possibly a NAD + NADP)‐dependent to a NADP‐dependent form of the enzyme. A diagram for a feed‐forward activation of the NADP‐linked dehydrogenase which possibly takes part in regulation of CO2‐fixation is presented.
The Role of Endogenous Lipid in Gluconeogenesis and Ketogenesis of Perfused Rat Liver
Authors: Menahan L. A. , Wieland O. 
Published: March 2005

The oral antidiabetic glycodiazine (2‐benzene sulfonamido‐5‐β‐methoxyethoxy pyrimidine), an inhibitor of hepatic lipolysis, was used to investigate the metabolic role of liver lipid in gluco‐genesis in the perfused livers of fasted (24–30 h) rats. In a concentration of 10 mM, glycodiazine inhibited almost completely endogenous ketone body formation.
Perfusion with pyruvate as substrate, in the presence of glycodiazine, resulted in a higher rate of pyruvate oxidation and suppressed the rate of glucose synthesis in comparison to livers perfused with pyruvate alone. Thus, maximal rates of gluconeogenesis from pyruvate would seem to require an adequate supply and oxidation of fatty acids.
Oleate, even in the presence of glycodiazine, stimulates glucose synthesis from pyruvate. Uptake of and ketone body formation from oleate were also not affected by glycodiazine. These results allow the conclusion that glycodiazine specifically inhibits liver lipolysis.
Glucagon (57 nM), although having no significant effect on gluconeogenesis from pyruvate at this concentration, overcame the inhibitory effects of glycodiazine on glucose formation and suppressed the elevated pyruvate oxidation which results from the inhibition of endogenous lipid mobilization.
Glucagon, in the absence of added substrates, stimulated gluconeogenesis, urea production and ketogenesis. The increase in gluconeogenesis due to glucagon was not impaired by glycodiazine. This indicates that intermediates arising from fatty acid oxidation do not limit the rate of gluconeogenesis under these conditions.
Study on Metabolism of Phospholipids in Animal Tissues
Authors: Káš J. , Hladík J. , Šícho V. 
Published: March 2005

Metabolism of phospholipids in post mortem tissues of liver, kidney, spleen, and heart of guinea pigs was studied. The per cent composition of the individual groups of phospholipids in the above tissues in the fresh state and after a certain period of the dying process taking place under the described conditions is shown. Generally, one can state that phosphatidyl choline is the most important component of phospholipids in these tissues, in liver and in heart representing about 70% of the total amount. They are metabolized relatively faster, while sphingomyelin and phosphatidyl serine are metabolized most slowly. On the basis of the lipid phosphorus determination it is possible to conclude that within 24 h about 20–30% of the phospholipids are decomposed. During the following phase of the dying process no further pronounced decrease of phospholipids takes place. After this period the enzyme system splitting phospholipids is practically inactive. During the dying process an apparent increase of inorganic phosphorus can be observed, which indicates the decomposition of other phosphorus compounds in the course of this process.The relative representation of the individual groups of phospholipids in liver mitochondria is different from that of the whole tissue. Liver mitochondria contain a relatively higher amount of phosphatidyl ethanolamine, a lesser amount of phosphatidyl choline, lysophosphatidyl choline being totally absent.
Über multiple Formen der Hexokinase in Hefe
Authors: KopperschlÄGER G. , Hofmann E. 
Published: March 2005

Multiple forms of hexokinase have been detected by agar gel and polyacrylamide gel electro‐phoresis in crude extracts obtained from yeast cells of different strains. Electrophoretic mobility and number of enzyme forms depend on the conditions of cell disruption and vary with the respective yeast strain. Extracts from commercial baker's yeast, prepared by short‐time mechanical disruption contain two or three isozymes of hexokinase. Cell‐lysis by proteolytic procedures (toluene, extraction of dried yeast) changed the electrophoretic pattern profoundly.Between the exponential and the stationary phases of growth characteristic differences in the pattern of the two isozymes of hexokinase have been found.Five different strains of yeast revealed different patterns of hexokinase isozymes.Electrophoresis on polyacrylamide gels, using a concentration gradient of the polymer, indicated that the differences in the mobilities of these enzymes are presumably not caused by major differences in their molecular sizes. Trypsin caused an increase of electrophoretic mobility of one or both forms of the enzyme from baker's yeast.
Isolation of Three Acid Phosphatases from Wheat Germ
Authors: Verjee Z. H. M. 
Published: March 2005

Three different forms of acid phosphatase have been isolated from commercial wheat germ by ion‐exchange chromatography on DEAE‐cellulose.
The three components could not be separated by gel‐filtration, suggesting that the enzyme was homogeneous with respect to molecular weight. A molecular weight of 55000 was obtained for all the three isoenzymes, as determined by gel‐filtration on Sephadex G‐100 and Sephadex G‐200.
The isoenzymic nature of the three forms was suggested by differences in their pH optima, Michaelis constants, response to activation and inhibition, substrate specificities and electrophoretic mobilities.
The isolation procedure was readily adapted to the preparation of large quantities of the isoenzymes. These partially‐purified forms were electrophoretically indistinguishable from the three components which could be demonstrated in the original wheat‐germ extract.
La biosynthése des stérols dans les tissus de tabac cultivés in vitro
Authors: Benveniste P. , Hewlins M. J. E. , Fritig B. 
Published: March 2005

Tobacco tissues grown in vitro were fed with labelled acetic acid during 5, 30 and 150 min, respectively. 4, 4‐Dimethylsterols, 4‐methylsterols and sterols were extracted and purified and their specific activities were determined by acetylation of biosynthetically labelled alcohols with [3H]acetic anhydride of known specific activity.On the basis of the measured specific activities, a tentative scheme for plant sterol biosynthesis is proposed. In particular, cycloartenol appears to play a direct role in this biosynthesis. The conversion of cycloartenol into sterols appears to be a non‐specific process with several possible parallel routes. The linear scheme previously proposed, involving the following transformations : cycloartenol → methylene‐24 cycloartanol → cycloeucalenol → obtusifoliol →“lophenols”, etc., appears to be only one of the pathways followed in our material.
The Use of Procion Blue as a Molecular Probe in the Study of Ribosomal Structure
Authors: Hultin T. 
Published: March 2005

The triazinyl dye, procion brilliant blue MR, has a selective initial action on the proteins of rat liver ribosomes in situ, and can be used for detecting shielding effects in normal and modified particles. Alterations in the shielding pattern can be analyzed by disc‐electrophoresis.
Irreversible dissociation of the ribosomes in Mg2−‐deficient media makes a normally resistant protein (“protein 5”) available to the reagent. This unmasking occurs even in the cold.
When the particles are incubated at 35° in the presence of aminoacridines, or in media with increased ionic strength, another previously shielded protein (“protein 10”) is unmasked by a time and temperature dependent reaction.
The unmasking of protein 10 by incubation in media with increased ionic strength is partially reversible by a time and tempreature dependent reaction. Although some detachment occurs in connection with the unmasking, the reversibility is probably confined to non‐detached molecules. The activity of the particles of endogenous or poly U‐dependent amino acid incorporation is not seriously impaired under these conditions.
The experiments indicate that organic reagents can be used to provide information about protein location and structural alterations in ribosomes, which confirm and extend structural data obtained by use of proteolytic enzymes.
Structure de l'haptoglobine de lapin
Authors: Cheftel R. I. , Parnaudeau M. A. , Bourrillon R. , Moretti J. 
Published: March 2005

Phylogenic research on the haptoglobin of different animal species led us to study the structure of rabbit haptoglobin.Rabbit haptoglobin, whose homogeneity was checked according to several criteria, was submitted to hydrolysis by pronase (72 h, 39°, pH 8.2); the hydrolysate was then filtered through Sephadex G‐25, and the resulting glycopeptide fraction was separated on Dowex 50‐X2 (H+) into two parts, one (A) not retained by the resin, the other one (B) collected after elution with 0.5 M NaCl.Amino‐acid and carbohydrate composition, nature of end groups, and timing of sialic acid release, were determined on fraction A; from the amount of aspartic acid, the molecular weight was estimated to be no less than 2860.Fraction B, which amounted to one third of fraction A, could not be analysed on account of the insufficient quantity available.Quantitative paper electrophoresis at pH 3.5 and 6.2 yielded 8 glycopeptides from fraction A and 2 from fraction B. These various glycopeptides showed notable differences in their amino‐acid composition, mainly with respect to glutamic acid, proline, glycine and histidine. On the contrary, no significant differences were found in the carbohydrate composition, with the exception of the oses N‐acetylneuraminic acid ratio, which varies from 2 to 10.These results suggest 6 oligosaccharide units to be present in rabbit haptoglobin, as compared to 7 in human haptoglobin, bound to peptidic fractions varying in their amino‐acid composition in the neighbourhood of the carbohydrate‐peptide linkage. Although the precise nature of this bond has not been ascertained, it does not appear to be an O‐glycosidic one.
Desensitization of Yeast Phosphofructokinase to ATP‐Inhibition by a Protein Fraction from Yeast
Authors: Atzpodien W. , Gancedo J. M. , Hagmaier V. , Holzer H. 
Published: March 2005

A heat‐labile fraction from yeast is described which converts the ATP‐sensitive from of phosphofructokinase (Form s), inhibited by high concentrations of ATP, into a desensitized form (Form d), not inhibited by excess ATP. This desensitization reaction is time‐dependent.
Forms s and d are different, relatively stable forms of phosphofructokinase. Retaining their characteristic sensitivity or insensitivity to ATP, they can be fractionated by ammonium sulfate and acetone.
The heat‐labile fraction, desensitizing Form s to Form d, is neither dialysable nor ultrafiltrable. It is inactivated by trypsin treatment of the crude extract. It can be fractionated by ammonium sulfate and acetone. All these facts strongly suggest that the active principle is a protein.
The protein fraction from crude yeast extract desensitizing Form s to Form d, was about 50‐fold purified by treatment with protamine sulfate and fractionation with ammonium sulfate and acetone.
Besides the desensitizing protein, the conversion reaction is dependent on fluoride, AMP, ATP‐Mg++, and fructose‐6‐phosphate. Ado‐3′:5′‐P has no effect.
The Participation of Ornithine and Citrulline in the Regulation of Arginine Metabolism in Saccharomyces cerevisiae
Authors: Ramos F. , Thuriaux P. , Wiame J. M. , Bechet J. 
Published: March 2005

The pools of arginine, ornithine and citrulline have been measured under different conditions of growth in wild type and argR mutants (non‐repressible for ornithine transcarbamylase and four other enzymes of the arginine biosynthetic pathway). Comparing these pools with the level of ornithine transcarbamylase and the rate of growth one may conclude:

The arginine pool of a wild type strain growing on ammonium as nitrogen source is 18 mM; it increases to 72 mM by addition of arginine to the medium and causes 95% repression of ornithine transcarbamylase synthesis. In decreasing the pool to 3.7 mM by a bradytrophic mutation the differential rate of ornithine transcarbamylase synthesis increases 6 times.
When the pool of ornithine is increased by external addition of this amino acid or by using ornithine as the only nitrogen source a repression occurs which reaches 50 to 70% simulataneously with an intense reduction of the arginine pool (≤ 1.2 mM). This low pool may reach a growth limiting value. This shows the existence of a double control by arginine and ornithine. Lysine mimics ornithine.
The primary effect of argR mutation is not at the level of the arginine pool.
A double regulatory mutant, argR and cpaO (which confers non‐respressibility to carbamoyl‐phosphate synthetase) shows that the double control of arginine and ornithine also reaches this enzyme.
The strain bearing simultaneously the argR and cpaO mutations shows an intense distrurbance of metabolism leading to cessation of macromolecules biosyntheses and a loss of viability when basic amino acids such as lysine, ornithine, α‐γ‐diamino butyric acid or arginine are added to a culture growing on glutamate as nitrogen source.
Citrulline is shown to be used as nitrogen source via arginine, under these conditions the arginine pool increases to 190 mM, but does not produce the expected high repression. Citrulline or a derivative attenine repression.
The Nucleotide Sequence of Methionine Transfer RNAM
Authors: Cory Suzanne , Marcker K. A. 
Published: March 2005

The species of methionine tRNA which places methionine into internal positions of growing polypeptide chains, methionine tRNAM, was purified from Escherichia coli strain CA265 labelled with 32P by column chromatography on DEAE‐Sephadex and benzoylated DEAE‐cellulose. Sequence analysis of the products of complete and partial digestion of tRNAM by ribonuclease T1 and by pancreatic ribonuclease permitted the derivation of the total primary structure of this molecule.The sequence of methionine tRNAM is where U* is probably 4‐thio‐uridine, and , A* and X are unknown nucleotides.