bluuebunny/crossref_metadata_2025_split huggingface dataset:
Steroid Metabolism in Rats Given [1‐2H2E]Ethanol
Authors: Cronholm Tomas , Makino Isao , Sjövall Jan 
Published: March 2005

The incorporation of deuterium into bile acids and cholesterol in rats with a bile fistula given [1‐2H2]ethanol was studied by gas chromatography‐mass spectrometry. Deuterium‐labelling of cholic and chenodeoxycholic acids was observed with 0.03 g [1‐2H2]ethanol per kg body weight. The 5β position in both bile acids reached a deuterium excess of about 7 atoms per cent with 1 g [1‐2H2]ethanol per kg body weight. With this ethanol dose, the deuterium excess in the 3β position was 15 atoms per cent in chenodeoxycholic acid, and 9 atoms per cent in cholic acid. The deuterium excess in the 3β position of metabolites of 3‐keto‐5β‐cholanoic acid was about 13 atoms per cent. In the endogenous bile acids, several positions other than 3β and 5β were labelled, and the number of di‐ and trideuterated molecules relative to that of monodeuterated ones increased during the first 2 h after ethanol injection. Cholesterol in bile was also labelled in several positions, and the proportion of labelled molecules increased slowly to reach 8–14% 2–3 h after the injection of 1 g [1‐2H2]ethanol per kg body weight. The deuterium‐labelling of bile acids in positions other than 3β and 5β was greater than that of cholesterol. Fasting for 48 h, and fasting followed by glucose feeding had little influence on the deuterium incorporation into bile acids, where as pyrazole prevented it almost completely.The results indicate that deuterium is transferred from ethanol via NADH to the NADPH that is utilized in the biosynthesis of cholesterol and bile acids. The higher and more variable labelling of the 3β than the 5β position may be explained by isotope effects or by the ability of the 3α‐hydroxysteroid dehydrogenase, involved in the reduction of the intermediary 3‐keto steroids, to utilize NADH. The difference between biliary cholesterol and bile acids with respect to labelling in positions other than 3β and 5β indicates that these compounds do not originate from the same cholesterol pool.All metabolites of 3‐keto‐5β‐cholanoic acid carried a 3α‐hydroxy group. This indicates that the 3β‐hydroxy‐5β‐steroid dehydrogenase isoenzyme of alcohol dehydrogenase has no function in the reductive metabolism of bile acids. Furthermore, the increased production of NADH during ethanol metabolism did not induce a formation of 3β‐hydroxycholanoic acids.
Tyrosyl‐tRNA Synthetase of Escherichia coli
Authors: Chousterman Suzanne , Chapeville François 
Published: March 2005

Using purified Escherichia coli tyrosyl‐tRNA synthetase it was found that the enzyme is a dimer containing apparently identical subunits of molecular weight 47000.The study of the complexes formed between the enzyme and its substrates leads to the conclusion that there are two binding sites for tyrosyladenylate as well as for tRNATyr per molecule of enzyme. No binding of tyrosine alone could be observed, but a complex with ATP alone was characterized.
Reduced Bohr Effect in NO‐Ligated Chironomus Haemoglobin
Authors: Trittelvitz Eberhard , Sick Hinrich , Gersonde Klaus , Rüuterjans Heinrich 
Published: March 2005

The low‐temperature electron‐spin‐resonance spectra of the NO‐derivatives of the monomeric Chironomus haemoglobins I, III, and IV being nearly identical to each other, indicate rhombic symmetry of the innermolecular electric field. At gz= 2.003 nine hyperfine lines (ΔH= 7 G) of nearly identical intensity are observed in the presence of 14NO, while 15NO produces two hyperfine lines (ΔH= 30 G) both showing a further splitting into three superhyperfine lines (ΔH= 7 G). These hyperfine structures represent the interaction of the unpaired electron with the N‐nuclei of the 5th and 6th ligand.No changes of the electron‐spin‐resonance spectra were found in the range of pH 5 to 10, although haemoglobin III and IV are known to possess an alkaline Bohr effect. Thus in case of NO‐binding the Bohr effect is apparently reduced. With the aid of proton‐magnetic‐resonance studies of the Bohr proton binding site, His‐G2, in NO‐haemoglobin III it was demonstrated that the pK value of this group is shifted by only 0.15 units from that of deoxy‐haemoglobin. This shift is considerably lower as compared with that induced by CO‐ligation.
Freezing of Rat‐Liver Lysosomes to —196°C in the Presence and Absence of Dimethylsulphoxide
Authors: Osborne Jacqueline A. , Morris George J. , Lee Donald 
Published: March 2005

The latency of acid phosphatase and β‐glucuronidase in homogenates of rat liver, prepared in 0.25 M glycerol‐2‐phosphate (pH 7.0), decreased after freezing to –196 °C. The latencies obtained were virtually independent of cooling rate in the range of 2–225 °C/min and the latency of acid phosphatase always suffered a greater decrease than that of β‐glucuronidase.The fall in latency was always less in the presence of 7.5% (1.06 M) dimethylsulphoxide and and the protection afforded to the latency of acid phosphatase was greater than that given to β‐glucuronidase. The sedimentability of both enzymes responded to freezing in a manner similar to that found for latency.The sedimentability of acid phosphatase decreased after exposure to high concentrations of sucrose or glycerol‐2‐phosphate. We suggest that this response, as well as the decrease in latency found after freezing and thawing, results from osmotic pressure gradients which arise when normally non‐penetrating molecules enter the lysosomes under a high concentration gradient.The decrease in sedimentability of acid phosphatase after exposure to high concentrations of glycerol‐2‐phosphate was accompanied by a decrease in the specific total activity of the enzyme and it appears that this enzyme is readily inactivated in the presence of high concentrations of this substrate.
Inhibition of Acetylcholinesterase Activity by Aromatic Chelating Agents
Authors: Wermuth Bendicht , Brodbeck Urs 
Published: March 2005

Form B of acetylcholinesterase from toluene‐treated electric organs of the electric eel was inhibited in a non‐competitive manner by chelating agents such as 1,10‐phenanthroline, 8‐hydroxyquinoline, 2,2′‐dipyridyl and salicylic aldehyde. The apparent inhibition constants ranged between 1.3 mM and 4.8 mM. Secondary plots revealed hyperbolic inhibition for 1,10‐phenanthroline, slope‐parabolic‐intercept‐linear inhibition for 8‐hydroxyquinoline, slope‐linear‐intercept‐hyperbolic inhibition for 2,2′‐dipyridyl and a linear inhibition pattern for salicylic aldehyde.
The direct participation of metal cations in the catalytic process could be ruled out on the following basis: the inhibition of the enzyme by chelating agents was rapid and reversible; it did not show any time‐dependent irreversible inactivation. Excess metal did not reverse the inhibition: metal · chelate complexes inhibited the enzyme similarly or even stronger as did the complexing agents by themselves. No inhibition, even at concentrations up to 0.1 M was observed with EDTA.
With 8‐hydroxyquinoline at pH 6.0 non‐linear double‐reciprocal plots were observed. The Hill coefficients were 1.01, 1.20, 1.30 and 1.32 for 0, 0.75, 1.50 and 3.00 mM 8‐hydroxyquinoline.
The inhibitory effects of these compounds were explained in terms of hydrophobic adsorption of aromatic nuclei at the active center and in terms of structural similarities to the substrate. The type of inhibition observed by these compounds is indicative of co‐operative binding of these ligands to acetylcholinesterase.
Properties of the Calcium‐Independent ATPase of the Membranes of the Sarcoplasmic Reticulum Delipidated by the Nonionic Detergent Triton X‐100
Authors: Walter Horst , Hasselbach Wilhelm 
Published: March 2005

When the sarcoplasmic reticulum membranes are solubilized in Triton X‐100 their ATPases are modified: the calcium‐dependent ATPase is activated whereas the basic ATPase is inhibited.
Phospholipids are removed from the solubilized sarcoplasmic membranes completely by chromatography on a sepharose column equilibrated with Triton X‐100. Thereby the activity of the calcium‐dependent ATPase is abolished and cannot be restored by addition of phospholipids.
The delipidated ATPase preparation, exhibits only low activity, which is not dependent on calcium but on magnesium alone. This calcium‐independent ATPase is activated to the level of the calcium‐dependent ATPase both by unsaturated and saturated fatty acids, by anionic phospholipids and various synthetic lipids.
The enhancement of the ATPase activity produced by lipids is related to the binding of these compounds to the membrane protein in amounts comparable with those of bound Triton as demonstrated by dialysis experiments with dodecylsulfate. When the concentration of Triton in the medium is lowered, the dodecylsulfate/protein binding ratio increases, while Triton is detached from the protein.
The activation of the calcium‐independent ATPase by saturated fatty acids is dependent upon the chain‐length of these aliphatic compounds. Only the long‐chain fatty acids are strong activators. Moreover, the hydrophilic group of lipids affects maximal activities. No activation is observed with lecithin or dodecanol, while alkyl‐sulfates or ‐phosphates activate most effectively.
The calcium‐independent ATPase differs from the calcium‐dependent ATPase in that it is insensitive to N‐ethylmaleimide, dinitrodithiobenzoic acid or salyrgan. The enzyme is strongly inhibited by prenylamine, sodium azide and silver ions. Similarly low alkali salt concentrations produce a strong reduction of the activity.
The relative rates, with which the nucleoside triphosphates are split by the calcium‐independent ATPase, differ considerably. As observed for the calcium‐activated ATPase. The dependence on the substrate concentration suggests a positive cooperativity concerning Mg · ATP (Hill coefficient 1.46). 50%, of maximal activity is obtained at 0.25 mM Mg · ATP. The enzyme is strongly inhibited by Mg · ADP.
The Mechanism of Action of Methionyl‐tRNA Synthetase
Authors: Lawrence Françoise , Blanquet Sylvain , Poiret Maryse , Robert‐Gero Malka , Waller Jean‐Pierre 
Published: March 2005

The catalytic properties of native and trypsin‐modified methionyl‐tRNA synthetases were compared in the ATP‐PPi exchange reaction and in the reaction leading to aminoacyl‐tRNA formation performed under comparable experimental conditions.In the ATP‐PPi exchange reaction, the two forms of the enzyme are virtually indistinguishable with respect to ionic requirements and Michaelis constants for ATP and methionine, while V values are in a ratio of 2 to 1 in favor of the native enzyme.In the reaction leading to aminoacylation of tRNAfMet and tRNAmMet, the native and trypsin‐modified enzymes differ in several respects. In particular, a pronounced inhibition by ATP occurs with the native enzyme but not with the trypsin‐modified form. Also, the ratio of the V values measured under optimal conditions are closer to 4 than to 2, in favor of the native enzyme.The ionic requirements for the aminoacylation reaction were examined in detail. Spermine, spermidine and NH4Cl, but not KCl, are able to sustain the formation of methionyl‐tRNA in the absence of magnesium, albeit at lower rates than in its presence. A pronounced synergistic effect of MgCl2 on the reaction catalyzed in the presence of spermidine or NH4Cl is described.
Relative Rates of Degradation of Mouse‐Liver Surface‐Membrane Proteins
Authors: Gurd James W. , Evans W. Howard 
Published: March 2005

The relative rates of degradation of the proteins of liver membranes and soluble fractions were examined by using a double‐isotope labelling technique.
The proteins of plasma membrane and smooth microsomal fraction were more rapidly degraded than those of the mitochondrial and soluble fractions.
No great variation in the rates of degradation of the proteins of plasma membrane and microsomal subfractions was detected. The proteins of intercellular gap‐junctions (nexuses) were degraded slowly.
Extraction of plasma membranes with aqueous and organic solvents and detergents indicated that fractions known to be enriched in glycoproteins underwent more rapid degradation.
The high molecular weight components of liver plasma membranes and derivative fractions were more rapidly degraded than those of low molecular weight. Since glycoproteins predominated amongst the high molecular weight components of plasma membranes, the functional significance of this finding is discussed.
The Effect of Insulin and Growth Hormone on the Flux of Tracer from Labelled Lactate in Perfused Rat Heart
Authors: Mowbray John , Ottaway James H. 
Published: March 2005

l[2.14C]Lactate tracer was added at 30 min to the perfused rat‐heart preparation described in the previous paper. The specific activities of perfusate and tissue lactate and pyruvate were measured over the period up to 60 min.
Perfusate and heart lactate radioactivity equilibrated rapidly: not so perfusate and heart pyruvate.
No pyruvate was lost from the tissue: the sole precursor of perfusate pyruvate was lactate. In the presence of insulin all pyruvate taken up from perfusate was obligatorily reduced to lactate.
A proportion of pyruvate in the heart did not become labelled and there is good reason to believe this is not an artifact.
Rate parameters at different steps in pyruvate metabolism have been determined by computer modelling. Both hormones modify these parameters: in particular pyruvate dehydrogenase appears to undergo rapid 7‐fold activation.
The rate of exchange of label between lactate and intracellular labelled pyruvate was used to calculate the [NAD]/[NADH] ratios in the exchange compartment and in mitochondria. Both hormones reduced the ratio about 5 times by comparison with control. The results emphasise the disparity between perfusate lactate/pyruvate ratio and the redox potential of cardiac cytoplasm.
The data strongly support the compartmentization in more than one distinct cytoplasmic space of some glycolytic enzymes in cardiac tissue. The relationship of these “compartments” to heart morphology is briefly discussed.
Evidence is presented that growth hormone exerts a much greater rapid “insulin‐like” effect than has hitherto been suspected.
Formation of the Yeast Mitochondrial Membrane
Authors: Ibrahim Nader G. , Stuchell Robert N. , Beattie Diana S. 
Published: March 2005

Amino acid incorporation in vitro by isolated yeast mitochondria could be supported by either an external ATP‐regenerating system or by the respiratory‐chain‐linked synthesis of ATP. However, the incorporation rates obtained with ATP and succinate were almost double those obtained with the ATP‐regenerating system and were inhibited by either antimycin A or oligomycin. In either system, addition of chloramphenicol, erythromycin or ethidium bromide caused an 80–90% inhibition of incorporation, actinomycin D and cordycepin caused a 20% inhibition, while rifamycin or cycloheximide had no effect.The rate of amino acid incorporation in vitro by isolated mitochondria was not subject to glucose derepression. In contrast, the rate of cycloheximide‐insensitive protein synthesis into mitochondrial membranes in vivo was lowered over 90% in repressed cells. Analysis of the labeled mitochondrial membranes by sodium dodecylsulfate gel electrophoresis indicated that the products of mitochondrial protein synthesis were qualitatively identical, but quantitatively different, in glucose‐repressed and derepressed cells. For example, a two‐fold increase in labeling into both the two peaks of highest molecular weight as well as the peak of lowest molecular weight was observed in mitochondrial membranes obtained from repressed cells as compared to mitochondrial membranes obtained from partially and fully derepressed cells.The rate of amino acid incorporation in vitro as well as the labeling of mitochondrial membranes in vivo was stimulated 50—100% in partially derepressed yeast cells which had been grown in medium containing chloramphenicol for three hours, washed, and allowed to grow for one hour in fresh medium without chloramphenicol. The stimulation of labeling in vivo resulted in a threefold increase of labeling into the peak of lowest molecular weight with a concomitant decrease of labeling into the peaks of high molecular weight suggesting that the accumulation of mitochondrial proteins synthesized in the cytoplasm, when chloramphenicol is present in the medium, may stimulate the synthesis of certain specific mitochondrial proteins. Furthermore, growth of the cells in the presence of cycloheximide, which would result in a depletion of the pool of mitochondrial proteins synthesized in the cytoplasm, followed by growth in fresh medium without cycloheximide, resulted in a 50% decrease in the incorporation rate in vitro.
The Dissociation of Escherichia coli Ribosomes
Authors: Ball L. Andrew , Johnson Peter M. , Walker Ian O. 
Published: March 2005

A systematic study has been made of the dissociation into subunits of the ribosomes of Escherichia coli. By analytical ultracentrifugation, ribosomes were shown to be in dynamic reversible equilibrium with their subunits. This enabled a thermodynamic analysis to be made of the association‐dissociation reaction and of several factors which influence it: the concentration of monovalent and divalent cations, the presence of transfer RNA and supernatant factors, the pH, and hydrostatic pressure. The apparent change in free energy for the association in 10 mM sodium phosphate pH 7.0 was–17.4 kcal/mol. Association was accompanied by the net binding of magnesium ions or the net release of monovalent cations (potassium, sodium, or Tris ions). Circular dichroism measurements of ribosomes and their isolated subunits over a range of magnesium and potassium ion concentrations indicated that a change in the conformation of each subunit accompanied association. The change occurring in the 50‐S subunit was dependent on the presence of potassium ions, whereas the change in the 30‐S subunit was magnesium‐ion dependent. The conformational change in the 50‐S subunit was critical for the association‐dissociation reaction.Under ionic conditions which lead to ribosome dissociation one molecule of transfer RNA was released per 70‐S ribosome. This was an independent reaction which did not influence the subunit association‐dissociation equilibrium. The release of transfer RNA was accompanied by the net release of four magnesium ions, and occurred with an apparent change in the free energy of 20.8 kcal/mol.
Heterogeneity of NADPH‐Dependent Aldehyde Reductase from Human and Rat Brain
Authors: Ris Margret M. , von Wartburg Jean‐Pierre 
Published: March 2005

Four multiple molecular forms of NADPH‐dependent aldehyde reductase are isolated by ion‐exchange and gel chromatography from human brain. Using the same procedure two multiple forms of NADPH‐dependent aldehyde reductase are found in rat brain.
The molecular weight of two of the forms of human brain aldehyde reductase is 40000 and of the other two forms it is 44000.
Large differences with respect to substrate specificity with a wide range of aliphatic and aromatic aldehydes are observed between the multiple enzyme forms of each species.
All enzyme forms use NADPH as coenzyme; additionally one enzyme of each species can use NADH as well.
Classical inhibitors of aldehyde and alcohol dehydrogenase do not affect the activity of the multiple molecular forms of aldehyde reductase from human and rat brain, but psychoactive substances such as barbiturates and chlorpromazine as well as “biogenic” acids are inhibitory.
Étude spectroscopique de l'acide folique
Authors: Thiéry Corinne 
Published: March 2005

A spectroscopic study of folic acid (AB), pterin (A) and para‐aminobenzamide (B), using absorption, fluorescence, phosphorescence and electron spin resonance techniques, indicates the occurrence of spectroscopic differences between the behavior of solution of folic acid AB and equimolar solution of (A + B).The experimental evidence may be summarized as follows: a probable hypochromic effect on the highest energy bands, and a bathochromic shift (8 nm) over the whole absorption spectrum of AB, compared to that of (A + B); highly efficient quenching (more than 95%) of the fluorescence of components A and B in AB, compared to (A + B); disappearance of phosphorescent and paramagnetic signal of B in AB, but not in (A + B). The experiments are carried out on samples in aqueous solution at pH 5.6 (neutral, sparingly soluble, form of A and AB) and at pH 10.5 (ionic form of A and AB).These spectroscopic differences, observed between solutions AB and (A + B), suggest important intramolecular interactions between the two chromophores A and B in the molecule AB.A folded configuration, in which pterin A and the aromatic ring of B are held in proximity by several hydrogen bonds, seems in better agreement with spectroscopic data, than the generally accepted planar form, with hyperconjugation over the two main rings.
The Labilization of Hemoglobin by Cobalt
Authors: Schulman Herbert M. , Sidloi Rose , Martinez‐Medellin Jaime 
Published: March 2005

To elucidate a mechanism for cobalt‐stimulated globin synthesis in rabbit reticulocytes, the cells were incubated with 1 mM CoCl2 containing 60Co. Although the cells incorporated cobalt irreversibly, evidence for the synthesis of cobalt‐protoporphyrin was not obtained. More than 90% of the cobalt recovered in the cell cytoplasma was bound to the globin moiety of hemoglobin. Similar results were obtained with erythrocytes and purified hemoglobin incubated with 60CoCl2.By CM‐Sephadex chromatography and isoelectric focusing it was found that cobalt‐labelled hemoglobin differs slightly in charge from native hemoglobin, possessing a lower isoelectric point.It was also demonstrated that the heme in cobalt‐labelled hemoglobin is less firmly bound to globin than the heme in the native protein, and that the purified cobalt‐treated protein can stimulate globin synthesis in rabbit reticulocytes.It is postulated that in reticulocytes cobalt stimulates globin synthesis indirectly by labilizing intracellular hemoglobin.
Some Properties of “Light” Cytoplasmic Ribonucleoprotein of Mouse Plasmacytoma
Authors: GRECHKO Vernata V. , SACCHAROVA Natalia K. , GORJUNOVA Ludmila E. 
Published: March 2005

[5‐3H]Uridine incorporation into ribosomes and other postribosomal ribonucleoprotein particles has been determined in mouse plasmocytoma MOPC406 cytoplasm after cell wall disruption. It has been shown that a large part of the radioactivity after 40 to 90‐min incubation is localized in the postribosomal zone of the gradient. The question arises whether these particles are the result of nuclear leakage during cell disintegration or whether they are native to the cytoplasm. To clarify this we have compared the following characteristics of cytoplasmic and nuclear ribonucleoprotein particles: (a) sensitivity to sodium deoxycholate; (b) sedimentation patterns in sucrose gradients; (c) buoyant density values in CsCl gradient; (d) dynamics of precursors incorporation into cytoplasmic ribonucleoprotein particles RNA.All these results have been considered as supporting the cytoplasmic origin of cytoplasmic postribosomal ribonucleoprotein particles.