bluuebunny/crossref_metadata_2025_split huggingface dataset:
Characterization of a New Type of Arginase from Chicken Liver
Authors: Rossi N. , Grazi E. 
Published: March 2005

This paper reports the partial purification and characterization of a new type of arginase from chicken liver.The enzyme can be demonstrated only in less than 10% of a fasting chicken population, and has never been found in fed animals.The new arginase differs with respect to several properties (chromatographic behaviour, sedimentation coefficient, Km for arginine) from the arginase normally found in chicken liver and is more like the ureotelic arginase isolated from rat liver.
Rat Liver Phenylalanine Hydroxylase
Authors: Nielsen K. H. 
Published: March 2005

The activity of rat liver phenylalanine hydroxylase has been measured in systems which, in addition to the components necessary for hydroxylation, contained ascorbic acid and catalase. 6‐Methyl‐tetrahydropterine or the corresponding 6,7‐dimethyl compound was used as tetrahydropterine cofactor. Simple kinetic experiments lead to the determination of rate constants for the following reactions: the aerobic oxidation of the tetrahydropterine cofactor, the reduction of the dihydropterine cofactor by ascorbic acid and other reductants and the conversion of the dihydropterine cofactor from an active to an inactive form. These rate constants are used for the calculation of the actual concentration of tetrahydropterine cofactor in the hydroxylase system and for correction of the measured rates of hydroxylation for the inactivation of the dihydropterine cofactor.Ascorbic acid, as well as other reductants that may be present, increase the instability of phenylalanine hydroxylase, but this effect is negligible at sufficiently high catalase concentrations. Certain non‐reducing inhibitors can also stabilize the enzyme.The initial rate of reaction at 30° is linear during the first 5 or 6 min. In contrast at temperatures of 25° and below there is a lag period, whose duration may be reduced by preincubation of the enzyme with tetrahydropterine cofactor. A similar preincubation of the enzyme with l‐phenylalanine seems to activate the hydroxylase briefly.
The Threonine‐Sensitive Homoserine Dehydrogenase and Aspartokinase Activities of Escherichia coli K 12
Authors: Truffa‐Bachi P. , van Rapenbusch R. , Janin J. , Gros C. , Cohen G. N. 
Published: March 2005

The complex protein carrying the two threonine sensitive activities aspartokinase I and homoserine dehydrogenase I is composed of six subunits of a molecular weight 60,000. Furthermore, quantitative determination of the N‐terminal amino acids indicates the presence of six methionine residues per mole of native enzyme (mol. wt. 360,000).Equilibrium sedimentation studies of N‐ethylmaleimide treated protein shows that its six disulfide bridges, revealed by chemical analysis, are intra‐chain.Fingerprints of tryptic digests of the protein fail to reveal any difference between the subunits.
Ion Transport in Liver Mitochondria
Authors: Rossi E. , Azzone G. F. 
Published: March 2005

The relationship between translocation of K+ and respiration has been studied under conditions where large variations of the transmembrane K+ concentration gradient were obtained. It is found that the energy expenditure is a function of the number of ions translocated and not of the transmembrane concentration gradient. The K+/∼ ratio is slightly below 3 when measured on the total oxygen uptake and between 3 and 4 when measured on the Δ oxygen uptake.
The maximal [K+]i/[K+]o ratio maintained by respiring liver mitochondria is about 1,600 corresponding to an equilibrium potential of 192 mV. When the [K+]i/[K+]o ratio exceeds 2,000 times addition of valinomycin under aerobic conditions causes an efflux instead of an uptake of K+.
Mitochondria behave as perfect osmometers in a wide range of osmolarities. It can be calculated that the concentration of osmotically active internal K+ corresponds to 45% of the total osmolarity of the medium.
The pH 6 Acetolactate‐Forming Enzyme from Serratia marcescens
Authors: Malthe‐Sørenssen Didrik , Størmer Fredrik C. 
Published: March 2005

The pH 6 acetolactate‐forming enzyme from Serratia marcescens has been purified to homogeneity, and some of its characteristics have been described.Cocarboxylase and manganese have been completely removed from the enzyme. The addition of FAD to the enzyme did not stimulate the formation of acetolactate, and no FAD was released from the enzyme after trichloro‐acetic acid treatment.The enzyme did not crystallize as the same enzyme from Aerobacter aerogenes does, but the kinetic properties of the enzyme are similar. The pH optimum in acetate is 6.0, and the enzyme activity is inhibited by phosphate and sulfate. These compounds cause sigmoidal kinetics, and apparent Michaelis kinetics are observed in acetate.
Studies on the Interaction of the Inhibitor O‐Mercuriphenyl β‐d‐Galactoside Chloride with β‐Galactosidase from Escherichia coli K12
Authors: Loontiens Frank G. , Wallenfels Kurt , Weil Rudolf 
Published: March 2005

The effect of the sulfhydryl reagent O‐mercuriphenyl β‐d‐galactoside chloride (synthesis given) on β‐galactosidase from Escherichia coli K 12 was investigated in view of the suggestion by Wallenfels and Malhotra in 1960 that cysteine participates in the catalytic mechanism of the enzyme. This reagent inactivated β‐galactosidase in amounts smaller than 8 sulhydryl equivalents, corresponding to one tenth of the total amount of protein SH groups. No change in the ratio of hydrolase and transferase activities was found in the partially inactivated enzyme. Competitive inhibitors were partially protective and inactivation could be reversed with 2‐mercaptoethanol.It was established that O‐mercuriphenyl β‐d‐galactoside chloride could not be regarded as an active site directed reagent for β‐galactosidase. The compound is enzymatically hydrolyzed and its reaction product O‐mercuriphenyl chloride is a more effective inhibitor than the galactoside itself.The sedimentation behaviour of the inactivated enzyme was comparable to the native enzyme. Yet upon standing, the modified protein tended to dissociate into the monomer of molecular weight 130 000 and to aggregate.The modified and inactivated enzyme still exhibited a strong binding capacity: 4 independent binding sites and a dissociation constant equal to 21 μM for the competitive inhibitor 3‐nitro‐4‐aminophenyl β‐d‐thiogalactoside were found by ultracentrifugation studies with absorption optics.Although some SH groups seem to be indirectly involved in enzyme function, it is evident that their modification, resulting in inactivation, does not significantly reduce substrate binding in the tetramer and that no SH group is involved in the catalytic mechanism itself.
Immunochemical Studies on Hen's Egg‐White Lysozyme
Authors: Strosberg Arthur D. , Kanarek Louis 
Published: March 2005

By specific chemical modification of amino acid residues of egg white lysozyme it is demonstrated that the carbamylation of the α amino group and carboxymethylation of the unique histidine residue do not affect the reaction of the enzyme with the anti‐lysozyme antibodies.In contrast, it appears from this work that carbamylation or acetylation of the ɛ amino groups, carboxymethylation of the methionine residues as well as CNBr cleavage of the polypeptide chain do alterate the antigenic structure of lysozyme.
Protonated Polynucleotide Structures
Authors: Sarocchi Marie‐Thérèse , Courtois Yves , Guschlbauer Wilhelm 
Published: March 2005

The interaction between poly(C) and guanylic monomers (guanosine, Guo‐5′‐P, Guo‐3′‐P and Guo‐2′/3′‐P) at millimolar concentrations was investigated by optical methods.
All monomers formed complexes of stoichiometry of 1 guanosine for 2 cytidines although under sensibly different conditions: while guanosine, Guo‐3′‐P and Guo‐2′/3′‐P formed complexes stable over several pH units, the interaction between poly(C) and Guo‐5′‐P is only stable within 0.1 pH units. The reasons for this surprising behaviour must be searched for in a conformation of Guo‐5′‐P which differs from the other guanyl monomers.
All complexes observed follow cooperative binding. The interactions are only stable in the presence of a large excess of monomer. Nearest neighbour interaction energies computed are found to be between 2 and 3 kcal/mole, sensibly lower than found in polymer interactions.
From the results presented it appears that the poly(C)‐guanyl monomer complexes have similar or identical geometry as poly(C) + poly(G) at acid pH.
Pools and Turnover Rates of Nuclear Ribosomal RNA in Tetrahymena pyriformis
Authors: Leick Vagn , Andersen Stig Bryde 
Published: March 2005

The labeling kinetics of rRNA in exponentially growing Tetrahymena pyriformis were analyzed quantitatively in order to determine pool‐sizes and turnover rates of nuclear 17 and 25 S rRNA.The mathematical analysis of the system indicates that, during the steady state of growth, there is an inverse proportionality between pool‐size and turnover rate of nuclear rRNA. Thus, from the labeling kinetics of rRNA and the growth rate constant (4.6 × 10−3 min−1), the pool‐size of macronuclear 17 S rRNA was estimated at 0.5% of that of cytoplasmic 17 S rRNA corresponding to a turnover rate constant of 0.92 min−1. The analogues figures for 25 S rRNA were estimated at 1.6% and 0.29 min−1.Since the RNA content of macronuclei is about 2% of the cellular RNA content, it is concluded that during growth, most nuclear RNA is found in precursors of ribosomes and that macronuclei contain few, if any, finished ribosomes.Apart from its use on rRNA, the method described here may be generally useful in determining pool‐sizes and turnover rates of other precursors, such as free ribosomal proteins.
The Compartmentation of CoA and Fatty Acid Activating Enzymes in Rat Liver Mitochondria
Authors: Skrede Sverre , Bremer Jon 
Published: March 2005

The effect of disulphides on acyl‐carnitine formation and fatty acid oxidation in rat liver mitochondria has been studied.
Tetrathionate, which does not penetrate the inner membrane, inhibited the carnitine dependent oxidation of long chain fatty acid oxidation almost completely. This oxidation was reactivated by CoA but not by other thiols.
Carnitine increased the inhibition by tetrathionate, indicating that a small pool of preformed acyl‐CoA is present at the outer membrane.
By means of a new, sensitive method for the determination of CoA, a leakage of CoA from the mitochondria during the incubations was demonstrated. The leakage was increased by Pi and 2,4‐dinitrophenol.
The observations in paragraphs 3 and 4 explain why carnitine stimulates the oxidation of fatty acids in the absence of added CoA.
It was confirmed that an ATP‐dependent fatty acid‐CoA synthetase with great capacity is localized in the outer mitochondrial compartment.
A small residual capacity for ATP‐dependent long chain fatty acid activation was demonstrated even in the presence of tetrathionate, indicating an “internal” localization. This activity may depend on the medium chain synthetase or on a separate enzyme in the matrix compartment. The activation of short chain fatty acids was not inhibited by tetrathionate.
Atractyloside inhibited both long chain acyl‐CoA synthetase and carnitine palmityltransferase. The inhibition of both enzymes was counteracted by CoA.
It is concluded that atractyloside is unsuitable for the study of the compartmentation of fatty acid activating enzymes in mitochondria.
From the studies with disulphides it is concluded that fatty acid oxidation in mitochondria can be explained by a simple two compartment model where the inner membrane is the permeability barrier. Such a functional model is in agreement with previous enzyme localization studies.
The Conformation of Small Proteins
Authors: Chicheportiche Robert , Lazdunski Michel 
Published: March 2005

The conformation of neurotoxin II of Androctonus Australis Hector has been studied by optical rotatory dispersion and ultraviolet difference spectrophotometry. Depending upon pH and temperature, the protein exists under, at least, four different molecular forms, I, II, III and D which are in rapid equilibrium.A state‐diagram has been obtained which describes the different zones of temperature and pH in which forms I, II, III and D are stable. A physico‐chemical analysis of all transconformations has been carried out. The acidic as well as the alkaline transition (I ⇌ II, and I ⇌ III respectively) are controlled by the unmasking of structurally important ionisable groups, one of them being probably the carboxylic side‐chain of an aspartic or a glutamic acid. Form I, which is predominant between pH 4 and 9 and below 30°, contains a high degree of ordered structure. It is very stable toward heat denaturation and remains folded in 9.5 M urea, while form II, its conformational isomer at acidic pH, is completely unfolded at 50° or in high concentrations of urea. A very low cooperativeness has been observed for the unfolding of form II in urea or at high temperatures.
Influence of pH and Metal Ions on the Fluorescence of Polycyclic Hydrocarbons in Aqueous DNA Solution
Authors: Green Brian 
Published: March 2005

The fluorescence of benzo[α]pyrene or perylene solubilized in DNA solutions of low ionic strength is strongly quenched either by addition of silver ions at a ratio Ag+:DNA phosphate < 0.15 or by lowering the pH from 7.5 to 5. In poly d(A‐T) solutions the effects are much less marked than in DNA. Cu2+ ions are also effective quenchers in this system and Co2+ and Ni2+ have some activity but little effect is seen with Mn2+, Zn2+, Cd2−, Mg2+ or Na+ ions.The results establish that GC pairs play the dominant role in these quenching reactions and show that the DNA bases have a specific role in the DNA/hydrocarbon interaction. They also suggest that GC‐containing sites are the major sites of physicochemical fixation of hydrocarbons to DNA.No gross difference in the general nature of the DNA binding sites was found for the carcinogenic benzo[α]pyrene and non carcinogenic perylene.
Substrate Specificity of Escherichia coli Peptidyl‐Transferase
Authors: Panet Amos , de Groot Nathan , Lapidot Yehuda 
Published: March 2005

The kinetics of the puromycin interaction with different ribosomal bound peptidyl‐tRNAs were studied. The rates of the puromycin reaction with AA‐Phe‐tRNA and AA2‐Phe‐tRNA using three different amino acids (AA) were compared. At 4° all the three dipeptidyl‐tRNAsPhe reacted considerably slower than the three tripeptidyl‐tRNAsPhe. Acetyl‐Phe‐tRNA reacted faster than the dipeptidyl‐tRNA, but slower than the tripeptidyl‐tRNA. Glyn‐Phe‐tRNA (n= 3, 6 and 9) reacted with puromyein much faster than Gly‐Phe‐tRNA and at a rate similar to that of Gly2‐Phe‐tRNA.Lauroyl‐Phe‐tRNA reacted with puromyein much slower than acetyl‐and octanoyl‐Phe‐tRNA both at 4° and 30°
Nachweis von Konformationsisomeren im Hämoglobin(III) von Chironomus th. thummi mit Hilfe der Elektronen‐Spin‐Resonanz
Authors: Gersonde Klaus , Sick Hinrich , Wollmer Axel 
Published: March 2005

The magnetic properties of oxidized haemoglobins from Chironomus th. thummi in the pH range, pH 5 to pH 10, are described.The results of magnetostatic susceptibility at room temperature show that the high spin part decreases from 80% to 70% during transformation of the H2O‐Hb(III) into OH‐Hb(III). Chromatographically purified individual haemoglobins do not differ in this regard from the complex material.The esr signals of the Hb(III) measured at 77° K, can be separated into three groups, according to their common pH behaviour. Each group of signals can be ascribed to one type of iron complexes each: (a) g⊥= 6, g= 2,00; (b) g1= 2.88, g2= 2.35, g3= 1.95; (c) g′1= 2.68, g′2= 2.16, g′3= 1.82.g is split into two signals with g1 = 2.03 and g2 = 1.98. g1 has a N‐hyperfine structure with five lines, g2 with three lines. These two g′ ‐signals are ascribed to two different conformation isomers of the native H2O‐Hb(III), which, dependent on the pH, can be transformed into each other. The half transformation point of this change of conformation at pH 7.2 is the allosteric pK value.The pH‐dependency of the g⊥ signal shows a biphasic curve, with inflection points at pH 6.9 and pH 8.9.By aid of a thermodynamic circuit process, the interaction between allosteric transformation and protolysis is described and the corresponding pK values are calculated from the pH dependency of g⊥.The mechanism of this allosteric interaction, that means of a proton binding site in the protein with the 6th ligand is discussed as a trans‐effect of the 5th ligand.
Echanges de lipides entre mitochondries, microsomes et surnageant cytoplasmique de cellules de pomme de terre ou de chou‐fleur
Authors: Benabdelkader Ahmed , Mazliak Paul 
Published: March 2005

The incorporation rates of [1‐14C]acetate in vivo into the lipids of different subcellular fractions of potato or cauliflower tissues are consistent with a flow of radioactive lipids from microsomes to mitochondria.When potato tuber microsomes, containing phospholipids labelled from [1‐14C]acetate, [32P]‐phosphate or [1‐14C]glycerol, are incubated in vitro with unlabelled mitochondria and cytoplasmic supernatant, the radioactivity of the microsomes decreases strongly within 2 hours; the lipids of the mitochondria and those of the supernatant become radioactive, taking up to 40% of the initial radioactivity. The same transfer of labelled lipids is observed when one incubates labelled mitochondria with unlabelled microsomes.During these experiments, one can observe a marked decrease of the specific radioactivities of the phospholipids present in the initially labelled fractions. This may be explained by a departure of labelled phospholipids from the radioactive fraction towards the other cellular fraction and by an arrival of unlabelled lipids from the initially unlabelled fraction to the radioactive fraction. The results obtained with three different precursors are roughly similar, suggesting that there is an exchange of entire phospholipidic molecules between the cellular fractions. However, the rates of exchange of the lipids labelled from [1‐14C]acetate are a little higher than those observed with the other precursors thus suggesting an exchange of free fatty acids in addition to the exchange of phospholipids.Phosphatidylcholine and phosphatidylethanolamine represent the most important fraction of the exchanged phospholipids.The cytoplasmic supernatant acts as an intermediate in these exchanges. When a volume of supernatant containing radioactive lipids is incubated with unlabelled mitochondria or unlabelled microsomes, the radioactivity of the supernatant lipids decreases. The lipids of the mitochondrial and microsomal fractions, particularly the phospholipids, become labelled.The results obtained when mixing cauliflower subcellular fractions in vitro are very similar.The same flows of lipid exchanges (in vitro) can be observed between potato mitochondria and cauliflower microsomes, or reciprocally. However, a great part of the lipids liberated by the cellular fraction from one species remains blocked in the cytoplasmic supernatant from the other species, which may indicate that the exchange are limited, in this case, by a specific requirement for certain kinds of lipids for the biogenesis of membranes.
Effects of Trialkyltin and Triphenyltin Copounds on Mitochondrial Respiration
Authors: Stockdale Martin , Dawson Alan P. , Selwyn Michael J. 
Published: March 2005

In a sucrose medium, free from anions which are effective in the anion‐hydroxide exchange catalysed by trialkyltins, the effects of these compounds on mitochondrial respiration are similar to those of oligomycin, i.e. inhibition of respiration coupled to phosphorylation, and of arsenate stimulated respiration. They do not inhibit respiration stimulated by uncouplers nor respiration stimulated by uptake of divalent cations. They do not induce significant light scattering changes in this medium.In a medium containing potassium chloride similar oligomycin‐like effects are observed but in addition some release of respiratory control and marked swelling of the mitochondria are observed. A time‐dependent inhibition of uncoupler stimulated respiration appears to be a secondary effect consequent upon extensive swelling. The maximal rate of respiration attainable by the uncoupling effect of the trialkyltin compounds is independent of which compound is used. The concentration of trialkyltin compound required to produce uncoupling is correlated with the concentration required to mediate the chloride hydroxide exchange.In media containing other anions the maximal rate of respiration produced by trialkyltin compounds is correlated with the rate of electrogenic uniport of the anions through the mitochondrial membrane.Uncoupling by trialkyltin compounds is attributed to the action of the anion‐hydroxide exchange followed by leakage of the anion out of the mitochondria. These two processes result in the discharge of both the pH differential and electrical potential difference across the mitochondrial membrane.Apart from a lytic action of triphenyltin chloride and a potent respiratory inhibition in the presence of iodide or thiocyanate ions, it is proposed that all the observed effects of those compounds can be accounted for by the oligomycin‐like inhibition and the mediation of an anion hydroxide‐exchange across the mitochondrial membrane.
Structure du virescenoside C, nouveau métabolite de Oospora virescens (Link) Wallr.
Authors: Cagnoli‐Bellavita Nera , Ceccherelli Paolo , Mariani Raffaele , Polonsky Judith , Baskevitch Zoïa 
Published: March 2005

Chemical investigation of the glycosidic constituents of Oospora virescens (Link) Wallr. resulted in the isolation of several glycosides. We have shown recently [1] that two of them, named virescenoside A (I) and B (II) are β‐d‐altropyranosides of virescenol A and B; these diterpenic aglycones have been found to have the structure of isopimaradien‐2α,3β‐19‐triol (IV) and isopimaradien‐3β,19‐diol (V), respectively [2].In this paper we describe the isolation and structure of virescenoside C, a new metabolite of Oospora virescens. The results obtained show that virescenoside C (IIIa), C26K40O7, m. p. 160—162°, [α]d− 71,4°, is a β‐d‐altropyranoside of virescenol C, which is found to have the structure of 3‐keto 19‐hydroxy isopimaradiene (VIa).These results are based on physical evidence (infra‐red, nuclear magnetic resonance and mass spectra) and particularly on the chemical correlation with virescenol B and virescenoside B.Virescenoside C seems to be the third example of an altroside found in nature.