bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of Pyruvate Carboxylase in Rat Liver Mitochondria by Adenine Nucleotides and Short Chain Fatty Acids
Authors: Walter P. , Stucki J. W. 
Published: March 2005

The activity of pyruvate carboxylase of intact rat liver mitochondria was measured by improved methods under various experimental conditions. In agreement with previous work, elevated ADP concentrations in the medium caused a strong inhibition of the enzyme activity. A partial reversal of this inhibition was observed upon addition of octanoate or decanoate, but not with octanoyl‐l‐carnitine. Furthermore, atractylate completely reversed this inhibition whereas dinitrophenol or oligomycin increased it. In these experiments, no clear correlation between pyruvate carboxylase activity and the levels of adenine nucleotides of the whole medium was apparent. However, the measurement of the intramitochondrial adenine nucleotide levels revealed a close inverse relationship between ADP levels and pyruvate carboxylase activity, as fatty acids and atractylate lowered whereas oliogomycin elevated the intramitochondrial ADP levels. Other evidence indicates that the intramitochondrial ATP to ADP ratio may also be of importance in regulating the pyruvate carboxylase activity. In the experiments with octanoate, the intramitochondrial AMP was strongly elevated and the ADP plus ATP pool was smaller. In agreement with this finding, the amounts of rapidly exchanging adenine nucleotides were found to be smaller in the presence of octanoate than in its absence, as measured by the incorporation of added [14C]ATP. The addition of octanoyl‐l‐carnitine caused only small changes in the intramitochondrial adenine nucleotide pattern and had also no significant effect on the incorporation of added [14C]ATP into the mitochondria.The solubilized mitochondrial pyruvate carboxylase could also be inhibited by ADP but this inhibition could not be reversed by octanoate nor with high amounts of acetyl‐CoA.Oxygen uptake measurements with intact mitochondria showed a strong increase in the rate of respiration upon addition of octanoate or octanoyl‐l‐carnitine to the ADP supplemented system. This increase could be inhibited by oligomycin indicating that the stimulated respiration is coupled to an increased phosphorylation of ADP.It is concluded that the pyruvate carboxylase activity is regulated mainly by the level of intramitochondrial ADP. The lowering of the intramitochondrial ADP level and the resulting stimulation of pyruvate carboxylase by fatty acids is related on one hand to the production of intramitochondrial AMP by fatty acid activation resulting in a lowering of the ADP plus ATP pool, and on the other hand to the increased utilization of ADP for oxidative phosphorylation.The possible physiological implications of these findings are discussed.
The Stability of a Codon Transfer RNA Complex
Authors: Högenauer Gregor 
Published: March 2005

Equilibrium dialysis experiments indicate complex formation between the trinucleotide ApUpGp and tRNAfMet, the dissociation constant of the complex being approximately 150 μM. Unfractionated tRNA containing only minute quantities of tRNAMet fails to form complexes with ApUpGp to a detectable extent thus suggesting that the binding ability for this triplet is displayed solely by methionine accepting tRNAs.Deacylation of tRNA appears not to interfere with its complex forming ability. The strength of a trinucleotide—tRNA interaction is not altered measurably if the terminal phosphate group is detached from the triplets.The observed binding phenomenon is interpreted as a codon—anticodon interaction in the absence of ribosomes.
Amino‐acylation du tRNA1Val de Escherichia coli par la phéenylalanyl‐tRNA synthétase de levure
Authors: Taglang R. , Waller J. P. , Befort N. , Fasiolo F. 
Published: March 2005

Comparison of the known primary structures of several tRNAs reveals striking similarities between the nucleotide sequences of yeast tRNAphe and Escherichia coli tRNA1Val. On the assumption that such structural analogy might lead to aminoacylation of both tRNAs by each of the corresponding aminoacyl‐tRNA synthetases, a detailed study of this system was undertaken.The results indicate that under optimal conditions, E. coli tRNA1Val can be completely aminoacylated by yeast phenylalanyl‐tRNA synthetase, while the reciprocal (i.e. valyl‐tRNAPhe (yeast) formation by E. coli valyl‐tRNA synthetase) could not be demonstrated under any of a variety of conditions tested.Conditions for Phe‐tRNA1Val (E. coli) formation by yeast phenylalanyl‐tRNA synthetase differ radically from those leading to aminoacylation of tRNA in homologous systems. In particular, the final yield of aminoacyl‐tRNA varies with enzyme concentration and is markedly affected by the nature of the buffer and the pH, as well as by the presence of monovalent cations and organic solvents such as ethanol and dimethyl sulfoxide. Similar observations have already been reported in the study of the aminoacylation of tRNA in several heterologous systems.The results are discussed in relation to the structure of the two tRNAs.
A Steady‐State Kinetic Investigation of the Reaction Mechanism of the Tryptophan Synthetase of Escherichia coli
Authors: Creighton Thomas E. 
Published: March 2005

The initial rate of glyceraldehyde‐P formation catalyzed by the tryptophan synthetase of Escherichia coli from indole‐3‐glycerol‐P has been measured as a function of the concentrations of indole‐glycerol‐P, serine, tryptophan, and indole. The conversion of indole‐glycerol‐P to indole and glyceraldehyde‐P is proposed to proceed by the ordered sequential release from the enzyme of indole followed by glyceraldehyde‐P. Tryptophan does not appreciably inhibit this reaction.
Tryptophan formation is proposed to occur by the random sequential addition of serine and indole‐glycerol‐P to the enzyme. Tryptophan is a product inhibitor of the reaction, apparently combining with the free enzyme and also forming an enzyme‐(indole‐glycerol‐P)‐tryptophan deadend complex.
Indole inhibits non‐competitively with respect to both indole‐glycerol‐P and serine, and is proposed to combine with the free enzyme and with the enzyme having bound indole‐glycerol‐P, serine, or both substrates.
The implications of the results for the catalytic center and subunit structure of the enzyme are discussed.
Glycannes liés à la fraction insoluble de la cornée de roussette (Scyliorhinus canicula L.)
Authors: Moczar Elemer , Moczar Madeleine 
Published: March 2005

The distribution of the heteropolysaccharide chains in the insoluble tissular network of the dogfish cornea was investigated. For this purpose, the corneas were extracted with a buffer solution composed of 1 M CaCl2, 0.05 M tris and 0.02 M citric acid to remove soluble proteins. The residual insoluble stroma was successively hydrolysed by collagenase and pronase. The glycopeptides obtained were separated by gel filtration and high voltage electrophoresis. Two types of sugar chains were detected:(a) polyosides composed of galactose, glucose, mannose, glucosamine, fucose, xylose and sialic acid, some of them at least linked to aspartic acid (type 1);(b) galactose or glucosidogalactose linked to hydroxylysine (type 2).For one heteropolysaccharide chain of type 1, 6 galactosidohydroxylysines and 4 glucosidogalactosidohydroxylysines were found.The insoluble stroma was submitted to a fractionated extraction procedure by trichloroacetic acid and water in order to remove all collagenous material. The residual structural glycoprotein exempt from hydroxyproline was hydrolysed by pronase and the glycopeptide fraction was isolated by exclusion chromatography and electrophoresis. A single major glycopeptide fraction of the type 1 containing galactose, glucose, mannose, xylose and glucosamine was obtained.This clear‐cut separation of the two types of glycopeptides by the tricholoroacetic acid treatment indicates that they are bound to different peptide chains: glycane of type 1 is bound to the peptide chain of structural glycoproteins (insoluble in hot trichloroacetic acid) and the glycane of type 2 is bound to the peptide chains of collagen (soluble in hot trichloroacetic acid).
Röntgenkleinwinkel‐Untersuchungen an der Fettsäuresynthetase aus Hefe
Authors: Pilz I. , Herbst M. , Kratky O. , Oesterhelt D. , Lynen F. 
Published: March 2005

Fatty acid synthetase, a multienzyme complex from yeast, was analysed by small angle x‐ray scattering. The molecular weight determined by this method (2.2 × 106) was in close agreement with the value determined earlier by ultracentrifugation.The experimental data indicate that the complex is contained in a ellipsoid volume with axial ratios 1:1:1.2. The relationship of radius of gryation to volume and the height of the second maximum in the scattering curve suggest that the complex proteins enclose a hollow space.A model is proposed where the theoretical scattering curve closely aggrees with the curve measured for the fatty acid synthetase. The model consists of a spherical shell, composed of spheres, having an average wall thickness of 20 Å and divided in half by a planar wall also 20 Å thick. The outer radius is 125 Å. On the basis of this model the catalysis of fatty acid synthesis by the synthestase is discussed.
Effect of Ethanol Metabolism on Redox State of Steroid Sulphates in Man
Authors: Cronholm Tomas , Sjövall Jan 
Published: March 2005

Ethanol intake has been shown to cause a rapid increase of the concentration of androst‐5‐ene‐3β,17β‐diol 3‐sulphate and a simultaneous decrease of the concentration of dehydroepiandrosterone sulphate in plasma. The ratio between the 17β‐hydroxysteroid and the 17‐ketosteroid increased with the ethanol concentration up to 30–50 mg ethanol/100 ml blood when a 6 to 10‐fold increase was obtained. The ratios between the 3‐sulphates of 5α‐androstane‐3α, 17β‐diol and androsterone and between the monosulphates of 5α‐androstane‐3β,17β‐diol and 3β‐hydroxy‐5α‐androstan‐17‐one also increased during ethanol metabolism. Deuterium was rapidly incorporated into the D‐ring of the three C19 steroid diols, reaching about 20 atom per cent excess 10 to 20 min after oral administration of 0.1 g [1‐2H2]ethanol per kg body weight. The concentrations of steroids with a sulphate group at C‐17 did not change and deuterium was not incorporated into these steroids or into the 17‐ketosteroid sulphates. The ratio between the 3‐sulphates of 5‐pregnene‐3β,20α‐diol and pregnenolone increased only slightly and incorporation of deuterium into the side chain of the C21 diol reached a maximum of about 4 atom per cent excess about 1 hour after the ethanol administration.The results indicate that the ratio between 3‐sulphates of 17β‐hydroxysteroids and the corresponding 17‐ketosteroids in plasma is determined by the NADH/NAD+ ratio in the liver cell cytoplasm. They also indicate that the 3‐sulphate of 5‐pregnene‐3β,20α‐diol is not formed from pregnenolone sulphate at the same site or with the use of the same coenzyme molecules as the 17β‐hydroxysteroids.
Der Testosteronstoffwechsel in der isoliert perfundierten Rattenleber
Authors: Staib R. , Sonnenschein R. , Staib W. 
Published: March 2005

The metabolism of testosterone was studied in perfused livers of normal male and female rats and of male rats, four days and four weeks after castration. The rats were treated twenty days with cyproterone acetate and cyproterone and four days with phenobarbital (Luminal). Livers were perfused with [4‐14C]testosterone (7.2 mg, 9 μC) in 250 ml Krebs‐Ringer‐bicarbonate solution. In some experiments the metabolism of testosterone was measured under perfusion conditions without oxygen and with addition of albumin in the perfusion medium.The isolated perfused rat liver shows a sex difference in the metabolism of testerone. The liver of females produces more 5α‐androstanediols than the liver of male rats. The quotient 5α‐/5β‐dihydrotesterosterone in females has a value of 2.63 and that in male rats is equal to 0.68. The production of 5β‐dihydrotestosterone is significantly smaller in female than in male rats. The quotient of the highly polar (H) and remaining metabolites (R) in male animals is 1.2 and that in female rats is only 0.5. The small quotient in the female rats is explained by the significant elevation of the remaining metabolites through the more active 5α‐reductase.Four days after castration of male rats, we can see a very significant decrease of the hydroxymetabolites (H) and a significant increase of the remaining metabolites (R). So we find a quotient H/R of 0.33 in the males as compared to that in the females (0.5). The elevation of the remaining metabolites, based on a significant increase in the production of 5α‐androstanediol is caused through an increase in the activity of 5α‐reductase after castration.We could observe a similar change in the metabolism in rat liver after four weeks castration, but the differences are not so marked as in four day castrated animals.After a twenty day application of cyproterone acetate, the metabolism of testosterone showed no important changes, except the absence of androstenedione. Application of cyproterone indicated a significant increase of the hydroxymetabolites. The reason for this will probably be found in an induction of the microsomal oxydases.After a four day treatment with phenobarbital (Luminal) the hydroxymetabolites show a significant increase, which can be explained by an induction of the microsomal oxydases.Under conditions without oxygen, the metabolism of testosterone significantly declines. As expected we find less highly polar derivatives.On addition of albumin to the perfusion medium, we observe a significant three fold increase in the metabolism of testosterone.
Nascent Subribosomal Particles in Tetrahymena pyriformis
Authors: Leick Vagn , Engberg Jan , Emmersen Julius 
Published: March 2005

The metabolism and physical‐chemical properties of nascent (precursor) 40 and 60 S subribosomal particles have been studied in exponentially growing Tetrahymena pyriformis GL.Analysis of formaldehyde‐fixed 40 and 60 S particles in isopycnic CsCl gradients reveals that they have a lower buoyant density than the corresponding 30 and 50 S ribosomal sub‐units. Moreover, overall labeling of the cells with [3H]amino acid and [32P]phosphate shows that the precursor particles attain larger 3H/32P ratios than the corresponding sub‐units, indicating that the precursor particles contain extra (accessory) protein that splits off when they are converted into ribosomal sub‐units. The extra protein constitutes 10 to 20% of the total structural protein.Experiments in pulse‐labeling with radioactive amino acids indicate that 40 and 60 S particles are very rapidly labeled. This suggests that, apart from the RNA moiety, at least part of the structural ribosomal protein moiety associated with the nascent particles is newly synthesized.The possible involvement of 40 and 60 S particles in sub‐unit exchange between rounds of translation was investigated by comparing their kinetics of labeling with that of the ribosomal sub‐units. The results of the comparison indicate that the rate of recycling of ribosomal sub‐units through the pool of 40 and 60 S particles is too slow to account for sub‐unit exchange between each round of translation.
The Nature of Inhibition of Mitochondrial Malate Dehydrogenase by Thyroxine, Iodine Cyanide and Molecular Iodine
Authors: Varrone Stelio , Consiglio Eduardo , Covelli Italo 
Published: March 2005

The mechanism of inhibition of the enzyme activity of mitochondrial malate dehydrogenase by thyroxine, iodine cyanide and molecular iodine has been further investigated. The results obtained allow us to exclude formation of a protein/inhibitor stable complex, iodination of the enzyme or disaggregation of the protein molecule into inactive subunits as explanations for the enzyme inactivation induced by the iodine‐containing compounds. On the other hand, it has been demonstrated that in all cases the enzyme inhibition is dependent on the oxidation of certain—SH groups necessary for the activity.Direct oxidation of the thiol groups of the protein by molecular iodine and iodine cyanide can be easily assumed, whereas the chemical mechanism of the thyroxine‐induced enzyme inactivation is harder to explain. However, since neither hormone deiodination nor metal chelation occur, while thyroxine by itself is also able to oxidize the thiol group of reduced glutathione, a direct effect of thyroxine on the sulfhydryl groups of the enzyme is postulated.
Inhibition of Protein Synthesis in the Reticulocytes by Aminoacyl Adenosine
Authors: Harbon Simone , Chapeville François 
Published: March 2005

Leucyl adenosine and phenylalanyl adenosine inhibited protein synthesis in the reticulocytes, inhibition being accompanied by the release of growing peptide chains from the ribosomes. The action of aminoacyl adenosines was compared to that of puromycin.Although leucyl adenosine was rapidly hydrolyzed in the incubation medium, inhibition was maintained within the reticulocytes for several hours, indicating a stabilization of the compound inside the cell. Reversibility of the inhibitory effect was temperature dependent.Protein synthesis was inhibited less efficiently in the lysate than in intact cells; an enhanced hydrolysis of leucyl adenosine was noticed in the lysate.No specificity of the inhibition reaction was observed concerning the amino acid moiety (leucine or phenylalanine), whereas in the nucleoside part, adenosine was required.
Markers of the Variable and Constant Region of Human Lambda Immunoglobulin Chains
Authors: Tischendorf Frank W. , Tischendorf Margrit M. 
Published: March 2005

52 human lambda immunoglobulin chains could be divided into two antigenic subtypes, St(+) and St(–).St(+) type chains represent a homogeneous structural group differing from St(−) type proteins by characteristic subclass specific positions in the N‐terminal sequence of amino acids. St(+) proteins follow the “Ha” type sequence. St(+) type molecules are present in normal L‐chain preparations. 19% of normal lambda chains appear to consist of St(+) type molecules.St(−) type chains include at least two isotypic variants, following the “Bo” and “X” type sequence of amino acids respectively.The results point in the direction that 3 germ‐line genes, one st(+) and two st(–) genes, encode the specificity region of lambda polypeptide chains.No correlation between N‐terminal St markers and the lysine‐arginine interchange at position 190 of the C‐terminal half was found; thus evidence of the unigenic control of the lambda molecule was not provided.190Arg and 190Lys proteins do occur in the three major antigenic lambda chain subclasses.The possible allelic nature of the lysine‐arginine interchange at position 190 is discussed.
A Sequence of 50 Nucleotides from Coliphage R17 RNA
Authors: Rensing Ulrich F. E. , Schoenmakers John G. G. 
Published: March 2005

A sequence of 50 nucleotides of the RNA from coliphage R17 has been determined. It can be read through in only one translational frame. The sequence is not part of the coat protein cistron nor does it come from the untranslated sequences described so far.Two possible “hairpin” secondary structures have been constructed.The two‐dimensional technique on thin‐layer plates has been used to fractionate intermediates in limited exonucleolytic digests of two dodekamers which could not be sequenced by conventional techniques. The potential general use of this method has been discussed.
Affinity Labeling by m‐Nitrobenzenediazonium Fluoroborate of Porcine Anti‐Dinitrophenyl Antibodies
Authors: Franěk Františiek 
Published: March 2005

From the tryptic digest of γ‐chains of porcine anti‐dinitrophenyl antibody which has been affinity‐labeled by m‐nitrobenzenediazonium fluoroborate, an azotyrosine‐containing peptide consisting of 28 amino acid residues was isolated using affinity chromatography on Sepharose‐bound antibodies. The peptide contained a half‐cystine residue and a tryptophan residue, The thermolysin digest of this peptide yielded several shorter pep tides. The amino acid sequence in the vicinity of the half‐cystine was revealed by the finding of the peptide Leu‐Ser‐Cys(O3H). Azotyrosine was found in a nonapeptide, the amino acid sequence of which was characterized by the presence of more than one amino acid in most of the steps of sequential degradation.Comparison of the amino acid sequence in the vicinity of the half‐cystine residue and of the partial amino acid sequence of the azotyrosine‐containing nonapeptide with the known sequences of heavy chains of man, rabbit, mouse and guinea‐pig immunoglobulins showed that the labeled tyrosine of γ‐chains of porcine anti‐dinitrophenyl antibody is located most likely in the hyper‐variable section between half‐cystine 22 and tryptophan 36.
Interconversion of Pyruvate Dehydrogenase in the Isolated Perfused Rat Liver
Authors: Patzelt Christoph , Löffler Georg , Wieland Otto H. 
Published: March 2005

Active form and total activity of pyruvate dehydrogenase were measured in homogenates prepared from tissue samples obtained from the isolated rat liver during perfusion.In the absence of substrate, the active portion accounted for about 20% of total activity in livers from fed rats, whereas only about 10% were found to be active in livers from starved rats. These activities remained rather constant during a perfusion period of 120 min. Addition of 10 mM pyruvate to the perfusion medium resulted in an immediate, three‐fold increase of the active pyruvate dehydrogenase. A similar effect was exerted by 20 mM fructose, which is known to be rapidly converted to pyruvate in liver. 10 mM lactate led to a considerably smaller increase of pyruvate dehydrogenase activity as compared to the effects obtained with pyruvate or fructose. Total activities of the enzyme did not change significantly during perfusion.If the activities of active pyruvate dehydrogenase from livers perfused with and without substrate were plotted against medium pyruvate concentrations an exponential correlation could be observed.Addition of 2 mM oleate abolished the effects of fructose or pyruvate on the formation of active pyruvate dehydrogenase. The simultaneous addition of d‐(+)‐decanoylcarnitine inhibited the action of oleate, indicating that fatty acid oxidation is required for the inactivation of pyruvate dehydrogenase by interconversion of the active to the inactive form.The possible physiological significance of pyruvate and fatty acids in the regulation of pyruvate dehydrogenase interconversion is discussed.