bluuebunny/crossref_metadata_2025_split huggingface dataset:
Expression du génome chez les hybrides interspécifiques
Authors: Denis Herman , Brachet Jean 
Published: March 2005

The interspecific hybrid Arbacia lixula♂×Paracentrotus lividus♀ which stops developing at the onset of gastrulation, was previously found to contain much more DNA of maternal origin (P. lividus) than DNA of paternal origin. In spite of this, the RNA synthesized by the blocked gastrula hybridizes better with DNA of paternal type than with DNA of maternal type. An explanation of this observation was sought in the present paper by means of saturation and competition experiments. The higher affinity of RNA from the hybrid gastrula for paternal DNA could be due to the fact that RNA of paternal type is complementary to a longer portion of the corresponding DNA than RNA of maternal type. This explanation was not satisfactory since the number of genes of paternal type which are active in the hybrid is not very different from the number of genes of maternal type.In normal embryos of A. lixula and P. lividus, RNA from unfertilized eggs and from plutei was found to be less competitive against labeled RNA from gastrulae than gastrula RNA itself. Transcription of the genome is therefore partially stage‐specific. This stage‐specificity is maintained in the hybrid as far as transcription of the maternal genome is concerned, but is lost as far as transcription of the paternal genome is concerned. The hybrid gastrula was shown to synthesize more RNA molecules of A. lixula type than does the normal gastrula of this species, whereas RNA of P. lividus type is produced in equal amounts in normal and in hybrid embryos. These observations explain the hybridization properties of the RNA synthesized by the blocked gastrula.The results suggest that the genes of paternal type that are very active in the hybrid are those genes which in normal embryos are transcribed at all stages of development and probably also in the adult. This class of genes is much more active in a foreign cytoplasm than in the cytoplasm of its own species. On the other hand, the genes whose activity is restricted to the gastrula stage in normal embryos are not active in the hybrid. This class of genes does not seem to function in a foreign cytoplasm.
Energy Production in Rat Parotid Gland
Authors: Feinstein Haim , Schramm Michael 
Published: March 2005

Rat parotid gland slices showed a very slow rate of glucose utilization and lactic acid production, both in the presence and in the absence of oxygen. Epinephrine, which caused rapid enzyme secretion by the slices did not affect the low rate of glycolysis.A rough calculation indicates that in the parotid gland ATP is produced by oxidative phosphorylation 50 times faster than by glycolysis. The mitochondria, when isolated and tested in presence of EDTA or EGTA showed respiratory activity and respiratory control comparable to those of liver mitochondria. Adenosine 3′ : 5′‐cyclic phosphate, which is an intermediate in induction of enzyme secretion, showed no clear‐cut effect on the functions of the parotid mitochondria. Isolation of the mitochondria in the absence of the above chelators yielded a preparation which was almost depleted of NAD, respired feebly on NAD linked substrates and showed no respiratory control. Addition of NAD+ restored respiration. The damage caused to these mitochondria during isolation was attributed to the high calcium concentrations found in the gland. Addition of small amounts of free calcium to functional parotid mitochondria indeed caused the loss of NAD and the decline of respiration. Tested in parallel experiments, liver mitochondria were much more resistant to added calcium. Their initial calcium content was one tenth that of the parotid mitochondria. The control of calcium distribution in the parotid gland and the possible functions of calcium are discussed.
Accumulation of Squalene during Hepatic Cholesterol Synthesis in vitro
Authors: Onajobi Funmilayo D. , Boyd G. S. 
Published: March 2005

The synthesis in vitro of cholesterol from dl‐[2‐14C]mevalonic acid by the rat liver 18000 ×g supernatant was studied. It was shown that in the presence of air and necessary cofactors, the 18000 ×g supernatant incorporated dl‐[2‐14C]mevalonic acid mainly into cholesterol plus cholesterol esters while a small percentage of the radioactivity was associated with squalene, squalene oxide, lanosterol and some unidentified products. However, when serum (rat or human) was added to the incubation mixture, the incorporation of dl‐[2‐14C]mevalonic acid into cholesterol was decreased, with a concomitant accumulation of radioactive squalene. There was a stoichiometric relationship between the concentration of serum in the incubation mixture and the decrease in cholesterol synthesis or the accumulation of squalene.Pretreatment of the serum by dialysis, heat, or reaction with p‐chloromercuribezoate (PCMB), and N‐ethylmaleimide, all failed to annul the squalene accumulating effect of serum.Fractionation of rat serum showed that an α1‐globulin possessed the squalene accumulating activity. Examination of Cohn fractions of human serum showed that the squalene accumulating activity was present in Fraction III‐0, Fraction IV‐1 and Fraction IV‐4. Delipidization of Fraction IV‐1 led to an increase in the squalene accumulating activity of this fraction.Purification of delipidized Fraction IV‐1 by a combination of ammonium sulphate precipitation, ion‐exchange chromatography and perchloric acid precipitation gave a fraction, active in accumulating squalene, with the mobility of an α1‐globulin (α1‐protein). Ultracentrifugal analysis showed that the α‐protein was composed of a major component whose sedimentation velocity was 2.1 Svedberg units and a minor component of higher sedimentation velocity. Incubation of α1‐protein with [14C]cholesterol led to the binding of these lipids to the protein. Comparison of α1‐protein with an apo‐protein of α1‐liporprotein obtained from Dr. A. Scanu (Chicago) showed that both had similar physical, chemical and biological properties, indicating that α1‐protein, the squalene accumulating factor of delipidized Fraction IV‐1, is the apo‐protein of α1‐lipoprotein.The present evidence indicates that the squalene accumulating factor of serum acts by binding squalene.
Localization of the Glycerol‐Phosphate Dehydrogenase in the Outer Phase of the Mitochondrial Inner Membrane
Authors: Klingenberg Martin 
Published: March 2005

Evidence for the localization of the mitochondrial glycerol‐phosphate dehydrogenase in the outer phase of the inner membrane is presented.

Glycerol‐phosphate does not permeate through the inner membrane to the matrix space in a number of mitochondria which actively oxidize glycerol‐phosphate.
The impermeability of the inner membrane to ferricyanide is demonstrated and this forms a basis for elucidating membrane localization of carriers.
In mitochondria from various tissues ferricyanide can interact directly with glycerolphosphate dehydrogenase but not with succinate dehydrogenase.
The oxidation of glycerol‐phosphate, in contrast to that of succinate, is insensitive to substrate depletion brought about by uncouplers.
The results are interpreted to show that both the substrate and the acceptor‐site of glycerol‐phosphate dehydrogenase are exposed to the outer side of the inner membrane. Thus, for the operation of the glycerol‐phosphate dehydrogenase, mitochondria do not require translocases for glycerol‐phosphate and dihydroxyacetone‐phosphate.
Maturation et intégration du RNA 5 S au cours de la biosynthèse de la particule ribosomale 50 S
Authors: Galibert F. , Eladari M. E. , Hampe A. , Boiron M. 
Published: March 2005

It is well known that protein synthesis is stopped either by chloromycetin or by starvation of an essential amino acid for a RCrel strain, ribosomal RNA synthesis continues but products do not appear in 50 S and 30 S ribosomes. It has also been shown that 5 S RNA synthesis is altered by the addition of chloromycetin but in an unknown manner. In this paper we report that:(a) during amino‐acid starvation of a RCrel strain of Escherichia coli, 5 S RNA is transcribed as 5 S relax RNA located outside the ribosomes, in the supernatant fraction;(b) this 5 S RNA which is slightly longer than the normal product is convertible into a true 5 S RNA when protein synthesis is restored after blockage of RNA synthesis by actionomycin;(c) part of the 23 S RNA from a 25 S particle appears after resumption of protein synthesis in a 40 S particle which contains normal 5 S RNA;(d) a pool of 5 S precursor RNA exists outside the 50 S ribosome. This 5 S precursor RNA is isolated;(e) this precursor which is isolated from the 105000 ×g supernatant fraction after pulse labelling, migrates on gel electrophoresis between 5 S relax RNA and true 5 S RNA.
The Phosphodiesterases in the Rat Pancreas
Authors: van Venrooij W. J. W. , Poort C. 
Published: March 2005

The purification of two phosphodiesterases found in the rat pancreas is described. The phosphodiesterase I, an enzyme of the snake venom type, has been purified about 500 times, the phosphodiesterase II, an enzyme of the spleen type, about 60 times. The phosphodiesterase I activity, optimal at a pH of about 9.0, is completely dependent on the presence of divalent metal ions. The phosphodiesterase II, being optimally active at a pH of around 6.0, does not show this dependency.RNA and oligonucleotides are degraded only to mononucleotides. The phosphodiesterase I liberates 5′‐mononucleotides, the phosphodiesterase II only 3′‐mononucleotides. Oligonucleotides ending on a 5′‐phosphate group and on a 2′‐phosphate group are preferentially degraded by the phosphodiesterase I; those ending on a 3′‐phosphate group by the phosphodiesterase II. Both enzymes readily degrade oligonucleotides ending on a cyclic 2′:3′‐phosphate group. The possible significance of the latter finding is discussed.
Chicken Liver Mitochondrial Phosphoenolpyruvate Carboxykinase
Authors: Felicioli R. A. , Barsacchi R. , Ipata P. L. 
Published: March 2005

Kinetic studies on the phosphoenolpyruvate carboxykinase (EC 4.1.1.32) catalyzed reactions (i. e. the phosphoenolpyruvate synthesis and the oxaloacetate HCO3− exchange) have been carried out with the use of a purified enzyme preparation. Intersecting initial velocity plots were obtained conforming to a sequential mechanism for both reactions.Competitive inhibition patterns were observed for both reactions with ITP as variable substrate and IDP as inhibitor. For oxaloacetate exchange reaction noncompetitive and mixed P‐enolpyruvate inhibition patterns were observed with respectively oxaloacetate and ITP as variable substrates.These results are consistent with an ordered kinetic mechanism where ITP is added first, followed by oxaloacetate, and the products are released in the order CO2, P‐enolpyruvate and IDP.A reaction mechanism involving the synthesis of a ternary transitory complex, common to both reactions, is postulated.
Isolement et propriétés des chaînes du DNA de bactériophage 2 C
Authors: Truffaut Nicole 
Published: March 2005

Bacillus subtilis phage 2 C DNA is double‐stranded, with a high molecular weight (about 100 million), a low Tm (77.8%), and a high buoyant density (1.742 g/cm3) in a CsCl density gradient. Denatured DNA centrifuged in a CsCl gradient reveals two bands (1.752 and 1.762 g/cm3) corresponding to the complementary strands.In this communication, we report preparative separation of two strands from denatured DNA, either by chromatography on a methylated albumin‐kieselguhr column, or by density‐gradient centrifugation in the presence of poly G. The melting curves of native and denatured DNA, and of isolated fractions before and after mixing and annealing, are compared. As shown by spectrophotometry, and by buoyant density, a good renaturation was obtained by mixing and annealing the “light” and “heavy” fractions; each isolated fraction cannot be renatured alone.Poly G strongly binds to the heavy fraction, increasing its density in a CsCl gradient by about 48 mg/cm3; there is also some binding to the light fraction (density increase under the same conditions, 6 mg/cm3). The resulting density difference between the two fractions is more pronounced than the natural one: 52 mg/cm3 instead of 10 mg/cm3. Poly C only interacts with the light fraction and host ribosomal RNA with the heavy one.Native DNA, and both fractions isolated by centrifugation in the presence of poly G, were analysed for base composition using 32P‐labelled DNA. Native DNA had a (G + C) content of 39.1%. As for the isolated fractions, there are more pyrimidines (cytosine, and hydroxymethyluracil replacing thymine) in the “heavier” fraction, which preferentially interacts with poly G.Both strands from infectious DNA were assayed for infectivity with negative results. The “renatured” DNA also gave negative results, probably owing to some natural or accidental breakage.
Identification of C19O2 and C21O2 Steroids in the Mono‐ and Disulphate Fractions of Human Faeces
Authors: Laatikainen T. , Vihko R. 
Published: March 2005

Steroid monosulphate and disulphate fractions were obtained from human faeces by chromatography on Sephadex LH‐20 and solvolysed. The steroids liberated were fractionated on silicic acid. Fractions containing C19O2 and C21O2 steroids were studied by thin‐layer chromatography, gas‐liquid chromatography and gas chromatography‐mass spectrometry.Dehydroepiandrosterone, 5α‐androstane‐3α,17α‐diol, 5α‐androstane‐3α,17β‐diol, 5α‐androstane‐3β,17α‐diol, 5α‐androstane‐3β,17β‐diol, 5β‐androstane‐3α,17β‐diol, 5‐androstene‐3α,17β‐diol, 5‐androstene‐3β,17α‐diol, 5‐androstene‐3β,17β‐diol, 5α‐pregnane‐3α,20α‐diol, 5α‐pregnane‐3β,20α‐diol, 5β‐pregnane‐3α,20α‐diol, 5β‐pregnane‐3β,20α‐diol,pregnenolone, 5‐pregnene‐3α,20α‐diol and 5‐pregnene‐3β,20α‐diol were found in the monosulphate fraction and 5‐androstene‐3β,17α‐diol as well as 5‐androstene‐3β,17β‐diol in the disulphate fraction of human faeces.Several steroids identified earlier in the disulphate fraction of human bile were found in the monosulphate fraction of human faeces, indicating partial hydrolysis of diconjugates in the intestine. The androstanediols and pregnanediols found in the faeces were primarily of a 3β‐hydroxy‐5α‐ or 3β‐hydroxy‐5β‐structure, whereas those in the bile were of a 3α‐hydroxy‐5α‐ or 3α‐hydroxy‐5β‐structure. This suggests conversion of a 3α‐hydroxyl to a 3β‐hydroxyl in the intestine in vivo.
Subunits of the Small‐Intestinal Sucrase · Isomaltase Complex and Separation of Its Enzymatically Active Isomaltase Moiety
Authors: Cogoli Augusto , Eberle Alex , Sigrist Hans , Joss Christine , Robinson Etheria , Mosimann Hugo , Semenza Giorgio 
Published: March 2005

The size and number of subunits of the sucrase · isomaltase complex (mol. wt approximately 220000) from rabbit small intestine were determined by dodecylsulfate‐polyacrylamide gel electrophoresis, gel filtration and fingerprint analysis of tryptic hydrolysates.It was found that two subunits of similar size (estimated mol. wt 110000 to 120000 each) build up the sucrase · isomaltase complex, the one carrying sucrase, the other isomaltase activity.The isolation of the active isomaltase moiety, along with small amounts of active sucrase as a byproduct, has been achieved.Amino acid and carbohydrate analysis of the two subunits are reported.
On the Mode of Activation of the Catalytically Essential Sulfhydryl Group of Papain
Authors: Polgár László 
Published: March 2005

The reaction of the thiol group of papain with chloroacetamide, iodoacetamide, d‐ and l‐2‐bromopropionamides was studied. In the acidic pH‐range the reaction rate is higher than expected for an ordinary SH‐group and shows a double‐sigmoid pH‐rate profile. In addition to the already described pKa of 8.5, we found a pKa of 4.0. This indicates that in the pH‐range where the enzyme is catalytically active the thiol group of Cys‐25 interacts with some amino acid side chain, presumably with the imidazole group of the neighboring His‐159. In the light of the X‐ray diffraction studies (Drenth et al., 1971), it is probable that the anomalous PKa of His‐159 is due to its interaction with Trp‐177.The comparison of the pH‐rate profiles of d‐ and l‐2‐bromopropionamide reactions indicates that there is no sifgnificant alteration in the geometry of the active site around pH 4, whereas at slightly alkaline pH structural changes can be observed. 2H2O has no effect on the rate constants of the alkylation reaction. This rules out the possibility of general base catalysis by the imidazole group of His‐159.The experimental data indicate that the dissociated thiol group forms an ion pair with the protonated imidazole group. On the basis of the formation of thiolate‐imidazolium ion pair, the mechanism of action of papain is reconsidered. It is concluded that the acylation and deacylation steps are not symmetrical processes, and they are one‐encounter type reactions. The interaction between His‐159 and Trp‐177 may be important in the catalysis.
A Simple Digital‐Computer Program for Estimating the Parameters of the Hill Equation
Authors: Atkins Gordon L. 
Published: March 2005

Fitting the Hill equation to experimental data for the kinetics of allosteric enzymes by using the linear regression of the Hill plot can produce unreliable results because of the uncertainty of estimating the value for the maximum velocity of the reaction.
The theory of a method and the flow diagram for a simple digital computer program are given so that the Hill equation may be fitted directly to experimental data by minimising a sum of squares of residuals. All three parameters of the equation are precisely determined.
The program was evaluated using artificial data simulated using the Hill equation and sets of normally distributed pseudo‐random numbers. The simulated error corresponded to coefficients of variation of 1, 2, 5 and 10%. The data were for 20 equally spaced, 10 equally spaced, 10 geometrically spaced and 6 geometrically spaced values of substrate concentration.
The Hill equation was fitted to these data sets using two published computer programs, the present program and an improved version of the Hill plot. The performances of these four methods were compared with respect to the precision and the bias of the sets of estimated parameters.
The precision of the parameter estimates was investigated with respect to the quantity, the precision and the spacing of data.
Conformational Studies on Lipoamide Dehydrogenase from Pig Heart
Authors: van Muiswinkel‐Voetberg H. , Visser Jaap , Veeger Cornelis 
Published: March 2005

Lipoamide dehydrogenase can be isolated as dimer in two forms: a dissociable and a non‐dissociable form. The non‐dissociable form has a higher activity. Both forms can be converted into each other.
The dissociable form can be converted into the non‐dissociable form, by heating to 70 °C, by treatment with NAD+, by alkaline pH or by 0.2 M phosphate buffer pH 7.2. The non‐dissociable form can be converted into the dissociable form by extensive removal of phosphate ions at low ionic strength, or freezing and thawing.
The monomer obtained upon dissociation is inactive. A reversible equilibrium exists between monomer and dimer; association constant 3–6 μM−1.
Dioxan and 2‐chloroethanol convert the enzyme into the dissociable form in a time‐dependent process. The rate of conversion is highly accelerated at high phosphate concentration. The presence of (NH4)2SO4, leads to denaturation.
Conformational Studies on Lipoamide Dehydrogenase from Pig Heart
Authors: van Muiswinkel‐Voetberg H. , Veeger Cornelis 
Published: March 2005

No structural differences could be detected between the dissociable and non‐dissociable dimer of lipoamide dehydrogenase from pig heart.
Optical rotatory dispersion and circular dichroism studies show that upon dissociation the protein undergoes conformational changes, very probably accompanied by changes in α‐helix content. The monomeric apoenzyme probably has a higher α‐helix content than the holoenzyme.
Treatment of the non‐dissociable enzyme with dioxan leads to monomerisation, accompanied by similar changes in optical rotatory dispersion and circular dichroism parameters in the 260 to 300‐nm region as obtained by spontaneous dissociation. The perturbation spectrum shows changes around a tryptophyl residue.
Dissociation leads to significant changes in fluorescence characteristics. The protein fluorescence emission increases upon dissociation, the energy‐transfer from tryptophan to FAD increases. It could be shown that one tryptophyl residue becomes more exposed.
Both the dimer and the monomer undergo a series of temperature‐dependent conformational changes.
Upon reconstitution the dimer from apoenzyme and FAD, conformational changes occur during more than 48 h.
Conformational Studies on Lipoamide Dehydrogenase from Pig Heart
Authors: van Muiswinkel‐Voetberg H. , Veeger Cornelis 
Published: March 2005

Lipoamide dehydrogenase binds sodium dodecylsulphate in its dimeric state at 25 °C in two phases. The first phase, 0–0.3 g/g protein, is bound purely to hydrophobic sites; the second binding phase, 0.3–1.4 g/g protein is less well characterized and is influenced by the ionic strength and the dissociation of a protonated group with pK 6.6. The effects can be reversed by cooling to 0 °C.
The spectral and kinetic parameters are only affected during the second binding phase, maximal effects are obtained, with the exception of fluorescence parameters, at 1.4 g/g protein. The changes in the absorption spectrum indicate that different parts of the flavin absorption spectrum are influenced by unequal dodecylsulphate concentrations. Fluorescence polarisation shows that FAD becomes less tightly bound. Upon prolonged incubation it dissociates.
Binding of dodecylsulphate has a large influence on the hydrodynamic parameters. Viscosity measurements indicate the existence of asymmetrical molecules; the sedimentation constant declines from 5.8 S to 2.6 S after an increase to 8.9 S. The results show that a dimeric dodecylsulphate · enzyme complex can be reactivated by removal of dodecylsulphate at 0 °C, the monomeric dodecylsulphate · protein complex remains inactive.
The Initiation of Protein Synthesis Directed by the RNA from Encephalomyocarditis Virus
Authors: Smith Alan E. 
Published: March 2005

The initiation of protein synthesis directed by the RNA from encephalomyocarditis virus in a cell‐free system from Krebs II ascites cells has been investigated.
Ascites cell Met‐tRNAMet donates all the internal methionyl residues of the viral‐RNA‐specified polypeptide, whereas little incorporation from Met‐tRNAfMet is detected.
fMet‐tRNAfMet, which is not normally present in the cytoplasm of eukaryotic cells, donates formylmethionine into polypeptide in response to the viral RNA to give a product which contains a single N‐terminal sequence fMet‐Ala‐Thr‐, and is identical to the normal cell‐free polypeptide except for the N‐terminal formylmethionyl residue.
Short‐chain peptidyl‐tRNA synthesised in vitro in response to encephalomyocarditis virus RNA in the presence of low concentrations of sparsomycin, which inhibits chain elongation but not initiation, contains the N‐terminal sequence Met‐Ala‐Thr‐.
This data supports the notion that unblocked Met‐tRNAfMet is the universal initiator of protein synthesis in eukaryotes and donates a methionyl residue into the N‐terminal position of all proteins. The initiating methionyl residue is in most cases subsequently removed from the nascent polypeptide, but this can be inhibited either by an N‐terminal formyl group or by preventing the nascent polypeptide from growing long enough to be a substrate for the methionine aminopeptidase.
The data also shows that encephalomyocarditis virus RNA, which codes for at least nine stable proteins in vivo, contains only one initiation site which is expressed in vitro. The polypeptide coded for immediately after the initiation site is not virus‐coat protein and is rapidly metabolised in vivo, suggesting that a lead‐in polypeptide precedes the first meaningful protein sequence.