bluuebunny/crossref_metadata_2025_split huggingface dataset:
Konformationsinduzierter Circulardichroismus in Hämoglobinen von Chironomus th. thummi
Authors: Wollmer Axel , Sick Hinrich , Gersonde Klaus 
Published: March 2005

The conformational isomers of Chironomus haemoglobin first postulated on the strength of the O2‐binding properties [24] and demonstrated by electron spin resonance spectroscopy [23] could now be confirmed by measurement of the circular dichroism.All the circular dichroism bands of the oxidized haemoglobin from Chironomus in the visible and Soret region are induced or influenced conformationally. The pH‐dependency of the extinction and the ellipticity of the individual bands follows a circuit process with four reaction steps, two of which describe the allosteric transformation and two the protolytic reaction of water at the 6th coordination point of the haem iron. With the aid of fit calculations we get the protolytic constants pK′2= 8.1 and pK”2= 8.3 and the allosteric constants pKa1= 7.3 and pKa2= 7.1.The existence of conformationally induced circular dichroism bands becomes obvious, if one compares the separated haemoglobins showing different degrees of allosterism. Thus for instance the individual haemoglobin IV, showing the smallest amplitude of the Bohr effect, is characterized by a minimal conformationally‐induced change of ellipticity. The individual haemoglobin VIII with the highest amplitude of Bohr effect shows the strongest conformationally‐induced circular dichroism bands.The pH‐dependency of the absorption spectra in the visible range displays further characteristics of conformational isomerism. The 4‐component system to be expected from the circuit process reveals at sufficient distance between the allosteric and protolytic pK values a system of two 2‐component mixtures, which can be transformed into each other depending on pH and thus produce “isosbestic triangles”.The helix content of the Chironomus haemoglobins is not influenced by the described change of conformation and amounts to 60 and 70% according to the individual haemoglobins.The results are discussed under the aspect of isomerism of conformations and allosterism controlled by the trans‐effect of the 5th ligand of the haem iron.
A propos de I'actomyosine et de quelques unes de ses propriétés physico‐chimiques
Authors: Arnaud Yves , Leger Jean J. , Gruda Julian , Leroux Louis 
Published: March 2005

The physicochemical properties of the actomyosin molecule were established by hydrodynamic and light‐scattering techniques. These results do not depend on the method of preparation.Taking advantage of aging of the solutions, and by taking into account the hydrodynamic pressure that acts during ultracentrifugation experiments, it is possible to obtain an homogenous analysis of the results of hydrodynamic and light‐scattering measurements. It seems likely that some discrepencies reported in the litterature may be explained by these observations.In solution, actomyosin is a cylindrical molecule whose main axis is about 5800 Å long, and 1160 Å in diameter; the molecular weight is about 18 ± 4 × 106; the greater part of this cylinder is occupied by solvent.Actomyosin is composed of F‐actin and A‐myosin which may be isolated by ultracentrifugation in the presence of ATP. In solution, actomyosin is a fibrillar molecule, whose axis is formed by F‐actin (4 × 106) and, on which 28 molecules of A‐myosin (5 × 105) are attached.A model for the structure of actomyosin in solution is proposed.
Studies on the α‐Methylglucoside Permease of Escherichia coli
Authors: Gachelin Gabriel 
Published: March 2005

The sequential events which occur in the membrane of Escherichia coli and lead to the antecedent appearance of α‐methylglucoside 6‐phosphate when cells are exposed to extracellular α‐methylglucoside have been analyzed.

It has been shown that phosphorylation is the rate limiting step in α‐methylglucoside phosphate synthesis in vivo. However, phosphorylation of α‐methylglucoside was not found to be the only step occurring in the thickness of membrane.
It was shown that a step of transport was necessarily taking place before phosphorylation. In the absence of phosphorylation (due to genetic inactivation of any part of the enzymatic complex devoted to phosphorylation, or to chemical inactivation of one among its components), this step was expressed as a facilitated diffusion of unaltered α‐methylglucoside. The demonstration of this facilitated passage rests on the following evidence: equalization of α‐methylglucoside concentrations in intracellular and extracellular compartments faster than when due to free passive diffusion alone; requirement of the interaction of α‐methylglucoside with a stereospecific site, distinct from EII, with a Km of 20 μM; finally, existence of counterflows suggesting that the passage was ensured by a mobile carrier, mediating both influx and efflux of α‐methylglucoside.
This step of stransport was shown to be required in intact cells for a normal efficiency of phosphorylation in vivo. However it was not expressed in vivo as a facilitated diffusion but very likely as a facilitated access to the site of phosphorylation of EII.
From these findings, and from an analysis of various mutants, it was concluded that a concerted change of conformation occurs when EII was phosphorylating, which renders the step of transport unlimiting. Some consequences of the dissociation of the α‐methylglucoside phosphate synthesis into two sequential steps are discussed. Mainly this model provides a simple explanation for the polarity exhibited by EII, the absence of phosphorylation of intracellular α‐methylglucoside and its continuous exchange.
Involvement of Intracellular Phospholipase C in Autolytic Fragmentation of Cytoplasmic Membranes of Bacillus cereus
Authors: Koga Yosuke , Kusaka Iwao 
Published: March 2005

Stoichiometry of changes in lipid composition during autolysis indicated that phospholipase C was involved in autolysis of the membranes of Bacillus cereus. Phosphatidylethanolamine and phosphatidylglycerol, which were main constituents of the membrane lipid, were hydrolysed by phospholipase C.The lipid‐rich material, which was released from the cell during autolysis, was found to be a kind of lipoprotein. Diglyceride, a product of phospholipase C, accounted for 69% of the total lipid in the released materials. Lipid/protein ratio of the material was calculated to be 1.56 (mg lipid/mg of protein). Electron microscopy of the material indicated that the material consisted mainly of membranous vesicles of about 0.2μm in diameter and had an “unit membrane” structure.From these results, it was concluded that the cytoplasmic membranes of B. cereus might be broken down at the site where phospholipid was hydrolysed by phospholipase C and the fragment was released into the medium.
Structure primaire de la caséine αS1 bovine
Authors: Mercier Jean‐Claude , Grosclaude François , Ribadeau‐Dumas Bruno 
Published: March 2005

Our previous studies [1, 2] on maleyl bovine αs1‐B casein were concerned with the isolation and amino acid composition of the tryptic peptides designated as Tm peptides. The sequence of the COOH‐terminal Tm peptide containing 48 residues was also reported.In the present study, we report the overlaps of all the cyanogen bromide peptides as well as the Tm peptides from αs1‐B casein.The αs1‐B casein which contains five methionyl residues was cleaved with cyanogen bromide. The six expected peptides obtained by this treatment and designated as CN peptides, were separated initially on Dowex‐50 X 2 and further purified by Sephadex column chromatography. The amino acid composition of these six purified CN peptides was determined. The results were in perfect agreement with the amino acid composition of αs1‐B casein deduced from the analysis of Tm peptides.The three Tm peptides from αs1‐B casein which contained methionyl residues were also cleaved by cyanogen bromide. The fragments obtained were purified by either paper chromatography or Sephadex column chromatography and the amino acid composition of these purified peptides was determined. Of the eight peptides thus obtained, three were found identical with the CN peptides obtained directly by BrCN treatment of the αs1‐B casein. The remaining three CN peptides from αs1‐B casein for which identical fragments could not be located in the Tm peptides, were digested with trypsin (in two cases after maleylation) and the resulting fragments were purified by Sephadex column chromaography. These tryptic peptides provided the remaining gaps. This permitted us to locate the relative position of all the CN peptides in the αs1‐B casein molecule. These results also indicate the location of all the Tm peptides except 2 in the αs1‐B casein molecule. Further, the chymotryptic peptides from one of the CN fragments of αs1‐B casein provided the missing overlaps.
The Active Site Cysteines of Thiolase
Authors: Harris J. Ieuan , Gehring Ulrich 
Published: March 2005

Inactivation of thiolase with iodo[1‐14C]acetamide has been shown to be due to its reaction with cysteine residues in the enzyme. [1‐14C]Carbamoylmethylcysteine was identified as the only product of the reaction and a study of the radioactive peptides that were isolated from a tryptic digest of the [1‐14C]carbamoylmethyl‐enzyme has shown that the reactive cysteines occur in a unique sequence extending to at least 26 amino acid residues in the primary structure.The enzyme‐substrate compound formed when thiolase reacts with [1‐14C]acetyl‐CoA is shown to contain [14C]acetyl groups bound in thioester linkage to at least three cysteines per mole. Moreover these residues of [14C]acetyl‐cysteine occur exclusively in a sequence that is identical to the sequence around the [14C]carbamoylmethylcysteine residues in the enzyme‐inhibitor compound, showing that the substrate and the inhibitior react with the same four cysteine residues in the enzyme.These results provide additional evidence for the chemical identity of the four subunits of thiolase.
The Partial Dissociation of Nucleohistone by Salts
Authors: Henson Patricia , Walker Ian O. 
Published: March 2005

The circular dichroism of calf thymus deoxyribonucleohistone was compared with that of samples partially depleted of histone in solutions of sodium chloride. Differences in the near ultraviolet circular dichroism of DNA and deoxyribonucleohistone were associated with the presence of the f2b, f2a2 and f3 histone fractions in the complex. The near ultraviolet circular dichroic spectra of both DNA and deoxyribonucleohistone were very sensitive to the solvent environment. Thus differences in the circular dichroic spectra of DNA and deoxyribonucleohistone cannot necessarily be associated with long‐range effects, such as supercoiling, but may be due to short‐range effects, such as might be caused by histone‐DNA interactions.The absorbance and the circular dichroic melting profiles of deoxyribonucleohistone were biphasic. A new dichroic species was formed during the melting of the first of these steps and evidence is presented that this is a new histone‐DNA complex produced by the migration of some or all of the fractions f2b, f2a2 and f3 from denatured to native regions of the DNA during the melting process. Thus the biphasic melting profile of deoxyribonucleohistone does not necessarily imply that these fractions are arranged heterogeneously on the DNA.
Metabolism of Steroids in Germfree and Conventional Rats Treated with a 3β‐Hydroxy‐δ5‐Steroid Oxidoreductase Inhibitor
Authors: Björkhem Ingemar , Gustafsson Jan‐Åke , Gustafsson Sven A. 
Published: March 2005

The 3β‐hydroxy‐Δ5‐steroid oxidoreductase inhibitor 2α‐cyano‐4,4,17α‐trimethyl‐5‐androsten‐17β‐ol‐3‐one was administered intramuscularly to germfree and conventional, male and female, rats. Under the experimental conditions used, no steroids were found in faeces and urine from the male rats, but a large number of steroids were identified in excreta from female rats. The following 3β‐hydroxy‐Δ5‐steroids, none of which is present in normal rats, appeared in urine and faeces from germfree and conventional cyanoketone treated female rats (chiefly as mono‐sulphates): 5‐androstene‐3β, 17β‐diol, 3β, 7α(and 7β)‐dihydroxy‐5‐androsten‐17‐one, 5‐androstene‐3β, 7α(and 7β), 17β‐triol, 3β, 16α‐dihydroxy‐5‐androsten‐17‐one, 3β, 17β‐dihydroxy‐5‐androsten‐16‐one, 3β‐hydroxy‐5,16‐pregnadien‐20‐one, 3β‐hydroxy‐17α‐pregn‐5‐en‐20‐one, 3β‐hydroxy‐5‐pregnen‐20‐one, 3β,7α(and 7β)‐dihydroxy‐5‐pregnen‐20‐one, 3β, 17α‐dihydroxy‐5‐pregnen‐20‐one, 3β, 16β‐dihydroxy‐5‐pregnen‐20‐one, 5‐pregnene‐3β, 16α, 20α‐triol, 5‐pregnene‐3β, 17α, 20α‐triol and 3β, 21‐dihydroxy‐5‐pregnen‐20‐one. In addition, several saturated steroids were identified which were identical with steroids excreted by normal germfree and conventional female rats.3β, 16α‐Dihydroxy‐5‐pregnen‐20‐one normally accounts for less than 1% of the total amount of 3β, 16α‐dihydroxy‐5‐pregnen‐20‐one and 3α, 16α‐dihydroxy‐5α‐pregnan‐20‐one found in urine. This percentage was found to be about 70–80 in urine from cyanoketone treated germfree as well as conventional female rats. This figure is in good agreement with the extent of inhibition (75–85%) of adrenal and gonadal (testicular and ovarian) 3β‐hydroxy‐Δ5‐steroid oxidoreductase found in experiments in vitro. It was established that the formation of saturated steroids from 3β‐hydroxy‐Δ5‐steroids in cyanoketone treated rats involved 3‐oxo‐steroids as intermediates since [3α‐3H,4‐14C]pregnenolone was converted into saturated steroids with loss of 3H. The hepatic 3β‐hydroxy‐Δ5‐steroid oxidoreductase active on C27 steroids was unaffected by treatment in vivo or in vitro with the cyanoketone.
Structural Studies on Ovine Growth Hormone
Authors: Peña Clara , Paladini Alejandro C. , Dellacha Juan M. , Santomé José A. 
Published: March 2005

The cyanogen bromide fragments obtained from ovine growth hormone have been isolated and chemically characterized. Two N‐terminal peptides 4 and 5 amino acids long and a C‐terminal dodecapeptide have been identified among them. The sequence of these fragments has been established and found identical to the corresponding peptides in bovine growth hormone.
All the information obtained gives further support to the already known analogy between ovine and bovine growth hormones.
Incorporation of Inorganic Phosphate into Phospholipids by the Homogenate and by Sub‐Cellular Fractions of Rat Liver
Authors: Williams Mary L. , Bygrave Fyfe L. 
Published: March 2005

Optimal incorporation of [32P]phosphate into phospholipids by rat liver homogenates requires the presence of NADH, Fru‐1,6‐P2 and of CMP. In the absence of 5 mM NADH and of 10 mM Fru‐1,6‐P2 little incorporation occurs.
Using the experimental conditions for optimal incorporation into the phospholipids by the rat liver homogenate, attempts to incorporate [32P]phosphate into the major phospholipids of mitochondria and of microsomes were undertaken. Incorporation into either microsomes or mitochondria alone was negligible. The addition of the cytosol (supernatant) to microsomes stimulated the incorporation but had little effect on the incorporation into mitochondria. Maximal incorporation of [32P]phosphate into the major phospholipids occurred only when mitochondria, microsomes and cytosol were present together in the reaction medium.
It is considered on the basis of these findings that the incorporation of the bases choline and serine into mitochondrial phospholipids observed in previous studies reflect exchange reactions and not de novo synthesis of the phospholipids by the mitochondria.
Factors Governing the Kinetics and Steady State of the Mitochondrial Nicotinamide Nucleotide Transhydrogenase System
Authors: Rydström Jan , Teixeira da Cruz António , Ernster Lars 
Published: March 2005

The mitochondrial nicotinamide nucleotide transhydrogenase catalyzes a rapid reduction of NAD+ by NADPH as compared to the reduction of NADP+ by NADH. By assuming pseudo first‐order kinetics it is shown that the rate constant of the reaction is strongly dependent on the actual [NAD+] [NADPH] / [NADP+] [NADH] ratio, giving a half‐maximal rate constant at [NAD+] [NADPH]/[NADH] [NADP+] of approx. 0.003. The altered rate constant can possibly be explained on the basis of a reversible conformational change of the enzyme between an active and an inactive state, controlled by the prevailing concentrations of oxidized and reduced nicotinamide nucleotides. Possible similarities with bacterial transhydrogenases are considered.In the presence of an energy source the overall transhydrogenase reaction involves a strong shift of the equilibrium towards the conversion of NADH and NADP+ into NAD+ and NADPH. Evidence is presented that the final extent of the overall energy‐linked transhydrogenase reaction is strikingly dependent on the ratio of the initial rates of the energy‐linked reduction of NADP+ by NADH and the nonenergy‐linked reduction of NAD+ by NADPH. Thus, the final extent of the transhydrogenase reaction in the presence of an energy source can by explained in terms of a steady state rather than an equilibrium. The possibility of an energy‐linked conformational change of transhydrogenase, involving a conversion of the enzyme from an inactive to an active state, is considered.
The tRNA Pyrophosphorylase Activity of Escherichia coli. A Study on Substrate Specificity
Authors: Gross Hans J. , Duerinck Fred R. , Fiers Walter C. 
Published: March 2005

tRNA pyrophosphorylase was partially purified from Escherichia coli MRE 600 cells. Upon chromatography on a DEAE‐cellulose column, two enzymatic activity peaks were partially resolved. Gel filtration indicated a molecular weight of approx. 42000 dalton for both. Some general properties are reported. The only consistent difference between the two enzyme fractions was that the first incorporated more AMP‐residues for a given tRNA preparation, as if the second has a more restricted specificity with respect to the acceptor tRNA molecules in the adenylation reaction.Partial degradation of tRNA by combined digestion with ribonuclease T1 and spleen exo‐nuclease indicated a rapid removal of approx. 16 nucleotides per tRNA molecule, presumably from more exposed regions. The amino acid acceptor activity was more sensitive to this nuclease pretreatment than the 3′‐terminal adenylic acid acceptor activity. Direct analysis showed that RNA fragments of chain length approx. 40 and even 10 were still functional in accepting terminal adenylic acid.
Association de RNA repidement marqué avec des structures cytoplasmiques dans les tumeurs plasmocytaires de la souris
Authors: Kempf Jules , Zahnd Jean‐Pierre , Mandel Paul 
Published: March 2005

The cytoplasmic fraction of mouse plasmocytoma cells contains messenger RNA‐protein particles similar to those called “informosomes” by Spirin [1,2]. Informosomes can be found in free form or bound to ribosomes, thus forming polysomes of buoyant density in CsCl ϱ∼ 1.55. In plasmocytoma cells, polysomes can in turn build up more complex structures of buoyant density ϱ∼ 1.4, by association with low‐density components of protein or lipoprotein nature.Evidence for the occurence of the different components in the ϱ∼ 1.4 density complexes is produced. Short‐time labelling and high sensitivity to mild ribonuclease treatment may account for the existence of messenger RNA. Presence of ribosomes and lack of membrane fragments are demonstrated by electron microscopic studies. Results obtained after detergent treatment favour the involvement of a lipoprotein fraction.It is noteworthy that the bulk of the short‐time labelled messenger sediments with the 1.4 density material, either as free informosomes, or as informosome‐ribosome‐lipoprotein complex. Our results combined with further studies suggest that the latter complex has a specific role in protein synthesis.
Hormone Action on Liver Adenyl Cyclase Activity
Authors: Hepp K. Dieter , Edel Roswitha , Wieland Otto 
Published: March 2005

Adenyl cyclase activity was measured by conversion of [32P]ATP to adenosine 3′:5′‐cyclic [32P]phosphate in a washed particle suspension from mouse and rat liver. The test contained an ATP regenerating system and 10 mM unlabeled Ado‐3′:5′‐P to trap the labeled Ado‐3′:5′‐P formed. Decreased activities were observed when methyl xanthines were used in place of unlabeled Ado‐3′:5′‐P. The reaction was stimulated by Mg++ which increased Vmax without changing the apparent Km towards ATP. Adenyl cyclase activity was stimulated by synthetic glucagon over the range of 0.1–20 μg/ml. Removal of Ca++ by ethylene glycol‐bis‐(β‐amino‐ethyl ether)‐N,N'‐tetraacetic acid (EGTA) strongly augmented glucagon action, while 1 mM Ca++ was inhibitory. The data suggest enhanced transmission of the hormone signal from the (hypothetical) receptor to the catalytic enzyme unit by chelation of membrane bound calcium.In contrast to the hyperbolic dose response curve observed with glucagon, the curve with fluoride (1–10 mM) was sigmoidal in shape, the effect being inhibited by 1 mM pyrophosphate. Although inhibition by Ca++ was observed, EGTA did not augment the effect of fluoride. The effects of fluoride and glucagon at maximal concentrations were not additive, indicating stimulation of the same adenyl cyclase system.
Studies on Rabbit Immunoglobulin Heavy Chains
Authors: Florent Gerard , van der Loo Wessel , Hamers Raymond 
Published: March 2005

Large peptides containing the allotypic determinants can be isolated from tryptic digests of rabbit IgG reduced with dithiothreitol.Their antigenic activity is detected by simple screening for interference in the allotype anti‐allotype reaction.Active peptides are obtained for A1 A2 and A3 allotypes and carry apparently the major determinants involved in the allotype anti‐allotype reaction.Further characterisation of these peptides is in progress.
The Phosphoglycerate Kinase Reaction and its Metal Ion Specificity
Authors: Larsson‐Raźanikiewicz Märtha 
Published: March 2005

The present study shows that MgATP2‐ or MnATP2‐ as substrates of phosphoglycerate kinase can be replaced by CaATP2‐, ZnATP2‐, CoATP2‐ or NiATP2‐. MnATP2‐ and NiATP2‐ are about 90% and 15%, respectively, and the other ATP4‐‐metal ion complexes roughly 70% as good substrates as MgATP2‐. No measurable activity was found with Be(II) or Fe(III). The effectiveness of the different substrate species appears to be determined by factors such as the size and polarizing capability of the metal ion as well as of the structure of the relevant metal ion complex and the rate of ligand dissociation processes.Detailed kinetics with Zn(II), Mn(II) and Co(II) showed that: (a) Zn2+ is a strong uncompetitive inhibitor of ZnATP2‐, Ki approx. 0.02 mM. (b) Mn2+ is a competitive inhibitor of MnATP2‐ at concentrations < 0.1 mM, Ki approx. 2.3 mM. This inhibition is dependent on the 3‐P‐glycerate concentration. At about 1 mM and higher concentrations Mn2+ acts as an uncompetitive inhibitor of MnATP2‐. (c) Co2+ is a competitive inhibitor of CoATP2‐ at about 1 mM and higher concentrations, Ki approx. 3 mM. With CoATP2‐ as substrate the activity is slightly increased in the presence of free Co2+ and/or free ATP4‐ at concentrations < 0.5 mM. When the CoATP2‐ concentration is varied, the activity seems not to become constant at concentrations ten times the apparent Michaelis constant for CoATP2‐.Equilibrium dialysis studies on the binding of Co2+ to the enzyme showed that this ion binds more strongly to the enzyme than, for example, Mn2+. This probably explains the differences in activation and inhibition observed with these two ions.The kinetic patterns obtained with the different metal ions indicate that Ni(II) behaves as Co(II), Cd(II) as Zn(II) and Ca(II) as Mg(II), which is somewhat similar in behaviour to Mn(II).