bluuebunny/crossref_metadata_2025_split huggingface dataset:
20β‐Hydroxysteroid : NAD Oxidoreductase Activity towards 3β‐Hydroxypregn‐5‐en‐20‐one Sulphate and Related Free Steroids
Authors: Pocklington T. , Jeffery J. 
Published: March 2005

The sulphate of 3β‐hydroxypregn‐5‐en‐20‐one is now reported to be a substrate for crystalline 20β‐hydroxysteroid: NAD oxidoreductase prepared from Streptomyces hydrogenans. Utilization of this steroid sulphate was not independent of activity towards pregn‐4‐ene‐3,20‐dione or 3β‐acetoxypregn‐5‐en‐20‐one, but the total rate of reaction for equimolar mixtures of 3β‐hy‐droxypregn‐5‐en‐20‐one sulphate and either pregn‐4‐ene‐3,20‐dione or 3β‐acetoxypregn‐5‐en‐20‐one was less than that calculated for the simplest type of mutual competitive inhibition, particularly at low substrate concentrations.The Michaelis constant for NADH was similar (about 5 μM) with each of these compounds as substrate.3β‐Hydroxypregn‐5‐en‐20‐one, and its 17α‐hydroxy derivative behaved anomalously, and their behaviour is discussed. 3β,17α,21‐Trihydroxypregn‐5‐en‐20‐one was a good substrate and had kinetic constants similar to those of 17α,21‐dihydroxypregn‐4‐ene‐3,20‐dione.
Action de la canavanine sur la synthèse du RNA chez E. coli
Authors: Simonnet G. M. , Chapeville F. 
Published: March 2005

Incorporation of uracil or UDP into RNA does not take place in Escherichia coli arg− RCstr in absence of arginine. Canavanine, a structural analogue of arginine, partially reestablishes RNA synthesis.In the strain E. coli arg− RCrel where RNA synthesis takes place in absence of arginine, canavanine shows inhibition. RNA synthesis will start again in this strain, if canavanine is removed from the culture medium. The presence of chloramphenicol together with canavanine suppresses the inhibitory effect of the latter upon RNA synthesis.In both arg− strains RNA synthesis will proceed, if nucleoside triphosphates are furnished to the bacteria. Canavanine has no effect on the utilisation of nucleoside triphosphates.The experiments reported suggest that canavanine acts upon the triphosphonucleoside kinases which appear to be inhibited by this arginine analogue in the relaxed strain.
Interactions of Ribosomal RNA with Synthetic and Natural Polybases
Authors: Krèumers P. , Fredericq E. 
Published: March 2005

The formation of complexes between RNA and calf thymus histone or polysine has been studied at molar ratios (basic groups to phosphoric groups) in the range 0.1 to 0.2.

The flexible polyelectrolyte behavior displayed by RNA in its reduced viscosity curves at low ionic strength disappears in the presence of the polybases.
The thermal profiles of RNA are shifted to slightly higher temperatures by the polybases.
Measurements of optical rotatory dispersion indicate an increase of ordered structure in the presence of the polybases, mostly polylysine.
Ultraviolet spectra of RNA have been measured from 186 to 300 nm, in native condition, at low ionic strength and at pH 3.2. Strong hyperchromic effects appear in the 188 nm absorption band under denaturing conditions. In the presence of histone or polylysine, the hyperchromic effects are markedly lowered.

It is concluded that both polybases combine to RNA, strengthening and extending the ordered areas and stiffening the molecular structure.
Étude par dichroïsme circulaire des interactions hème‐flavine‐protéine dans le cytochrome b2 (l‐lactate oxydoréductase) de la levure
Authors: Iwatsubo M. , Risler J. L. 
Published: March 2005

The circular dichroism spectra of bakers' yeast l‐lactate dehydrogenase and some of its derivatives (without flavin and/or heme) have been investigated in order to obtain some information about the interactions between the prosthetic chromophores or between these chromophores and the protein moiety.The following derivatives were studied: (a) the cytochrome b2 (flavohemoprotein), (b) the apocytochrome b2 (following FMN removal), (c) the noyau cytochromique b2 (low molecular weight core isolated following proteolytic degradation), (d) the apo‐noyau cytochromique b2 (obtained by removal of the heme from the latter).It is shown that the circular dichroism spectra of the protein moieties in the ultraviolet region (200–250 nm) are not affected, either by the removal of the flavin from the flavocytochrome b2, or by the removal of the heme from the noyau cytochromique b2. The significance of the values calculated for the α‐helical content is discussed. The oxido‐reduction state of the ferric ion does not affect the circular dichroism spectra in this region.The circular dichroism bands associated with the heme chromophore are essentially the same in the apocytochrome b2 and in the noyau cytochromique b2, i. e. both without the flavin moiety, but are markedly changed in the flavocytochrome b2, in particular with an inversion of the strong γ band.Noticeable differences are observed with a homologous enzyme extracted from the yeast Hansenula anomala, especially in the γ band region.In conclusion there appears to be no prosthetic group‐protein interaction detectable by circular dichroism measurements, i. e. no important modification of the peptide bond geometry occurs when the flavin is removed from the enzyme or when the oxido‐reduction state of the heme is varied. However, a strong effect is exerted by the flavin on the symmetry of the heme environment, this effect being probably an indirect one, via the protein moiety, as discussed in this paper.
Étude en culture continue du phénomène de répression transitoire
Authors: Gaillard R. 
Published: March 2005

A chemostat is used to study the kinetics of establishment of β‐galactosidase catabolite repression in unrepressed cultures of Escherichia coli. A state of catabolite repression near to zero is obtained in a continuous culture in which the growth is limited by the carbon source. An excess of carbon source is abruptly added into the culture vessel at the beginning of the kinetics. The transient repression phenomenona can be obtained both with a constitutive strain and with inducible strains in the presence of an inducer. They can be obtained with one substrate, the concentration of this substrate alone being changed during the kinetics.After a phase of severe repression of short duration, it is possible to observe another phase of resumption of the β‐galactosidase synthesis which does not follow the normal law of enzyme synthesis. During this phase the amount of β‐galactosidase is growing linearly as a fonction of time, while the cells are growing exponentially. The continuation of this linear synthesis is not affected by an abrupt slowing down of the cell growth. This independence between the β‐galactosidase synthesis and the growth can be explained by uncoupling between the transcription of the last messenger RNAs and their translation into enzyme. It must be assumed that during the linear synthesis the existing messenger RNA is stabilised by the physiological conditions of catabolite repression.
Factors in the Iodination of Histidine in Proteins
Authors: Wolff J. , Covelli I. 
Published: March 2005

Factors that determine the reactivity toward iodine of the histidyl residues of various proteins are compared. The proteins studied include lysozyme, ribonuclease, insulin, lactic, malic and glutamic dehydrogenases, phosphoglucomutase, thyroglobulin, trypsin, chymotrypsin and β‐lactoglobulin. Relatively fewer histidyl residues than tyrosyl residues are iodianated at pH 8.5 both in water and in guanidine. The fraction of iodine present in histidyl residues increases with increasing pH. Diiodohistidine is formed primarily in proteins that do not contain tryptophane.Thyroglobulin can be iodinated to contain 8% histidine iodine. However, mono‐ and diiodohistidine formation in equilibrium‐labelled thyroids accounts for < 1% of the total iodine.Histidine iodination requires the dissociable proton of the imidazole ring as shown by lack of iodination of N‐methylated model compounds. The assumption that iodination proceeds by an attack on the imidazole anion (rather than via an N‐I intermediate) is supported by the finding that the sterically hindered 2‐t‐butyl imidazole is iodinated.It is concluded that, although conformational factors such as electrostatic facilitation and ligand binding influence the reactivity of certain histidyl residues, the major factors in histidyl iodination are the instrinsic properties of the residue.
The Acylation of Diacylglycerols in Pig Liver
Authors: ÅKesson B. 
Published: March 2005

A pig liver microsomal fraction catalyzed the formation of radioactive triacylglycerols and 1,2‐diacyl‐sn‐glycerols when incubated with different X‐1,2‐diacylglycerols, ATP, CoA, MgCl2 and radioactive fatty acids.
Analysis of the radioactive diacylglycerols suggested that they were formed by acylation at position 1 of 2‐monoacylglycerols, which were produced by hydrolysis of the added X‐1,2‐diacylglycerols.
No difference between 1,2‐diacyl‐sn‐glycerols of different degree of unsaturation and various rac‐1,2‐diacylglycerols as substrates for triacylglycerol and diacylglycerol formation could be detected.
1,3‐Dioleoyl‐sn‐glycerol was about half as effective as rac‐1,2‐dioleoylglycerol as substrate for triacylglycerol synthesis and caused no formation of radioactive diacylglycerols.
Preparation of Crystalline Nucleoside Diphosphate Kinase from Baker's Yeast and Identification of 1‐[32P]Phosphohistidine as the Main Phosphorylated Product of an Alkaline Hydrolysate of Enzyme Incubated with Adenosine [32P]Triphosphate
Authors: Edlund B. , Rask L. , Olsson P. , Wålinder O. , Zetterqvist Ö. , Engström L. 
Published: March 2005

A nucleoside diphosphate kinase has been highly purified from baker's yeast, and has been obtained in a crystalline form from an ethanol‐containing medium. During short‐time incubation with [32P]ATP, the enzyme was phosphorylated to an extent of about 3–4 phosphoryl groups per mole of enzyme assuming a molecular weight of 105. This indicates an intermediate phosphorylation of the enzyme. 1‐[32P]Phosphohistidine was shown to be the dominating radioactive degradation product in an alkaline hydrolysate of the 32P‐labelled enzyme. In addition, 3‐[32P]‐phosphohistidine and Ne‐[32P]phospholysine were obtained in small amounts.The results indicate that the amino acid sequence around the reactive 1‐phosphohistidine of the yeast enzyme is different from that of human erythrocytic and bovine liver nucleoside diphosphate kinase.
Composition of Rat Liver Triacylglycerols and Diacylglycerols
Authors: ÅKesson B. 
Published: March 2005

Different fractions of rat liver triacylglycerols and X‐1,2‐diacylglycerols were prepared by thin‐layer chromatography on silver nitrate‐containing silica gel.
The positional distribution of fatty acids in these fractions and unfractionated triacylglycerols and diacylglycerols was analyzed by a scaled‐down version of Brockerhoff's method.
Both in tri‐ and diacylglycerols position 1 contains mainly saturated fatty acids, while most fatty acids in position 2 are unsaturated. Position 3 in triacylglycerols contains mainly unsaturated fatty acids and has a large proportion of highly unsaturated fatty acids.
The relative abundance of different 1,2‐diacyl‐sn‐glycerol units in diacylglycerols and triacylglycerols was similar except for highly unsaturated units. This suggests a random utilization of 1,2‐diacyl‐sn‐glycerols with 1–3 double bonds for triacylglycerol biosynthesis. The highly unsaturated diacylglycerols probably originate from phospholipids.
From the positional distribution of fatty acids in total triacylglycerols the proportions of different triacylglycerol fractions were predicted from the assumption that each fatty acid in any position is combined with fatty acids in proportion to their relative amounts in the other positions. The observed distribution agreed well with the predicted one‐.
Ribonucleoside Diphosphate Reductase. Purification of the two Subunits, Proteins B1 and B2
Authors: Brown N. C. , Canellakis Z. N. , Lundin B. , Reichard P. , Thelander L. 
Published: March 2005

Ribonucleoside diphosphate reductase from Escherichia coli B consists of two non‐identical subunits, called proteins B1 and B2. After purification from extracts of a partially derepressed thymine‐requiring mutant, both subunits were obtained in essentially pure form.Criteria of purity included the demonstration of constant specific enzyme activity in peaks from final chromatographic or electrophoretic steps and the behaviour of the proteins during ultracentrifugation and analytical gel electrophoresis.Determinations of molecular weights by sedimentation equilibrium centrifugation gave values between 160000 and 200000 for protein B1 and 78000 for protein B2. Evidence was obtained for some dissociation of protein B1 during centrifugation.Separately, each subunit was completely inactive; together, under the proper conditions, they catalyzed the reduction of the 5′‐diphosphates of cytidine, uridine, adenosine and guanosine to the corresponding deoxyribonucleotides.With the exception of deoxyadenosine 5′‐triphosphate, the regulatory effects of nucleoside triphosphates were identical to those observed earlier with less pure preparations of enzyme. The general inhibitory effect of deoxyadenosine 5′‐triphosphate at concentrations higher than 1 μM was obtained as before. In addition, lower concentrations of this nucleotide had a novel stimulatory effect on the reduction of cytidine diphosphate.
14CO2‐Bildung aus [3‐14C]Serin in roten Blutzellen
Authors: Rapoport S. , Müller M. , Knöfel R. 
Published: March 2005

Substrate‐free incubated erythrocytes and reticulocytes of rabbits form 14CO2 from [3‐14C]‐serine.
The 14CO2 formation from [3‐14C]serine exhibits a maturation‐dependent maximum, which is about ten times higher than that of erythrocytes.
The production of 14CO2 from [3‐14C]serine requires the splitting off of the hydroxymethyl group with formation of glycine. Serine undergoes neither desamination nor transamination. This is indicated by the fact that neither pyruvate, nor lactate or alanine are labelled. The β‐carbonatom of [3‐14C]serine is found in the porphyrines and the 14CO2 formed from serine is diluted by inactive formate.
In erythrocytes the 14CO2 is formed exclusively from formate by the peroxidative action of catalase. If catalase is irreversibly inhibited with 3‐amino‐1,2,4‐triazole the 14CO2 formation from [3‐14C]serine, is completely suppressed.
In reticulocytes there exists a second catalase‐independent pathway of 14CO2 formation from [3‐14C]serine, which is proposed to be as follows: condensation of formyl‐tetrahydrofolate with succinyl‐CoA with formation of α‐ketoglutar‐semialdehyde, its oxidation to α‐ketoglutarate and oxidative decarboxylation to succinate. This pathway is indicated by the dilution of 14CO2 from [3‐14C]serine by glycine and particularly by the incorporation of the β‐carbon‐atom of serine in α‐ketoglutarate.
Optical Properties of Oriented Dye‐LiDNA Complexes Prepared with the Wet Spinning Method
Authors: Rupprecht A. , Rigler R. , Forslind B. , Swanbeck G. 
Published: March 2005

For the study of the spatial arrangement of dyes bound to DNA a recently developed wet spinning method for DNA has been modified in order to prepare highly oriented dye‐DNA complexes. After bathing in alcoholic solutions containing LiCl and either acridine orange, proflavin or chrysazin, spun LiDNA deposits were dried and thereby coalesced into films of highly oriented dye‐LiDNA complexes. The method is reproducible and it is possible to obtain samples of practically any desired dimensions.The maxima of absorption and emission spectra were characteristic for these dyes when bound to DNA. The films exhibited a strong negative dichroism. The dichroic ratios indicated that the absorption vectors of these dyes would be inclined more than 65° to the DNA helix axis. Preliminary polarized fluorescence measurements have been performed using the recently developed method of Nishijima and coworkers. To analyze the fluorescence intensity curves the recent theoretical study of Desper and Kimura has been extended for uniaxial orientation (The Appendix) to account for the occurrence of non‐coinciding absorption and emission vectors of the single chromophoric group. The application of this extended theory to simple models indicated that the angles of inclination to the DNA helix axis of the absorption and emission vectors of acridine orange and proflavin would be confined to the interval 65°–90°. The angles between the absorption and emission vectors in these dyes were estimated to lie within an interval of 20°–30°. It is concluded that improved experimental conditions and use of a computer to analyze the polarized fluorescence curves would give more precise information.Wide‐angle X‐ray diffraction photographs of the specimens showed the undistorted crystalline B form pattern which might indicate that the dye molecules have not penetrated the DNA crystallites in the present modification of the wet spinning method. Other methods for introducing the complexing agents in the wet spinning method are discussed and the wide applicability of these samples of oriented DNA complexes for physico‐chemical studies is stressed.
The Conversion of N‐Formyl‐l‐Aspartate into Nicotinic Acid by Extracts of Clostridium butylicum
Authors: Scott T. A. , Bellion E. , Mattey M. 
Published: March 2005

The rate of synthesis of nicotinic acid by partially purified cell extracts of Clostridium butylicum was increased when the substrates l‐aspartate and formate were replaced by N‐formyl‐l‐aspartate. Aminopterin (0.2 mM) inhibited the synthesis from l‐aspartate and formate, but not from N‐formyl‐l‐aspartate. N‐Formyl‐d‐aspartate did not support the synthesis of nicotinic acid.
In the presence of aminopterin, radioactivity from 14C‐labelled N‐formyl‐aspartate was incorporated into nicotinic acid by partially purified cell extracts with only low dilution of the molar specific radioactivity.The pattern of labeling in the synthesised nicotinic acid showed that C‐2, 3, 7, and 6 of the nicotinic acid were derived from C‐2, 3, 4 and the formyl carbon of N‐formyl‐aspartic acid.
Partially purified extracts of Cl. butylicum synthesised N‐formyl‐aspartic acid from aspartate and formate and this formylation was inhibited by 0.2 mM aminopterin.
Thrombosthenin M
Authors: Cohen I. , DE Vries A. , Bohak Z. , Katchalski E. 
Published: March 2005

Thrombosthenin M was isolated from equine blood platelets by lysis of the platelets with n‐butanol at pH 7.0 at low ionic strength (I= 0.05), separation of the insoluble thrombosthenin by centrifugation, and extraction of thrombosthenin M from the sediment with 0.02 M pyrophosphate buffer pH 9.5. Contaminating ribonucleic acid was digested with ribonuclease and the protein finally purified by gel filtration on Sephadex G‐200. The purified thrombosthenin M was found to be free of thrombosthenin A and of fibrinogen. Thrombosthenin M, similarly to actin‐free muscle myosin, possesses a Ca++‐activated but not a Mg++‐activated ATPase activity, and shows neither a drop in viscosity nor superprecipitation on addition of ATP. Ultracentrifugal analysis of the thrombosthenin M preparation obtained (pH7.0, I= 0.6) revealed that about 90% of the protein sediments with a sedimentation coefficient of 7.2 S and about 10% with a sedimentation coefficient of 33 S. The thrombosthenin M preparation yielded a single band on disc electrophoresis; some of the protein failed, however, to penetrate the gel.Incubation of thrombosthenin M with thrombin resulted in the appearance of one mole of carboxyl terminal arginine per 105 g of thrombosthenin M. The ATPase activity of the thrombosthenin M was not affected by thrombin. Incubation of equine platelets with thrombin resulted in the disappearance of the electrophoretic band corresponding to thrombosthenin M. Antiserum against thrombosthenin M was found to inhibit the clot retraction of thrombin‐treated platelet‐rich plasma.
Labeling of α‐P of Nucleoside Triphosphates by in vivo Incorporation of 32P in Rat Liver
Authors: Landin R. M. , Moulé Y. , Gaye P. 
Published: March 2005

Rat liver RNAs labeled in vivo by 32P and hydrolyzed by snake venom phosphodiesterase into 5%‐nucleotides show a specific radioactivity always higher for AMP than that found for GMP, UMP and CMP. The difference of labeling is found on ribosomal and nuclear RNA as well as on the internal chain of tRNA.The high labeling of AMP of [32P]RNA compared to the other 5′‐phosphates is not due to contaminants but to the very high radioactivity of the α‐P of the ATP precursor in comparison to that of other nucleoside triphosphates, especially after a short incorporation time. The inequality of labeling decreases with time.
Metabolism and Excretion of C19‐ and C18‐ Steroids by Human Skin
Authors: Oertel G. W. , Treiber L. 
Published: March 2005

After intravenous administration of [7α‐3H]dehydroepiandrosterone [35S]sulfate (3H/35S = 2.88) to a normal male subject various 3H‐labeled C19‐ and C18‐steroid metabolites could be isolated from the fractions of free steroids and double‐labeled sulfoconjugates (3H/35S = 3.16) in skin extracts, containing a total of 1.36% of the injected 3H‐activity. The specific activity of 3H‐labeled steroids in skin extracts was found to be significantly lower than that of corresponding compounds in the 24‐hour urine.Whereas in skin extracts up to 95% of steroids present were isolated from the fractions of sulfoconjugates, more than 90% of steroids in sweat extracts could be detected in the fraction of free steroids.From such data, as well as from the qualitative and quantitative composition of steroid fractions in skin and sweat it was concluded, that under in vivo conditions endogenous sulfoconjugated dehydroepiandrosterone undergoes a direct metabolism in human skin tissue. Subsequently, sulfoconjugated metabolites probably suffer hydrolysis prior to excretion in sweat.