bluuebunny/crossref_metadata_2025_split huggingface dataset:
Absorption and Enterohepatic Circulation of Neutral Steroids in the Rat
Authors: Eriksson Håkan 
Published: March 2005

The absorption of labelled pregnenolone, corticosterone, pregnenolone sulphate and deoxycorticosterone sulphate after intragastric, intraduodenal and intracaecal injection was studied in female bile fistula rats. Efficient absorption was observed in all cases. Evidence was obtained for the absorption of both free steroids and sulphates from the small intestine, free steroids being absorbed more rapidly. Partial hydrolysis of the sulphates, probably bacterial, occurred in the intestine. Radioactivity in the portal blood was distributed between the free, glucuronide, monosulphate and diconjugate fractions. Glucuronides were present in the bile but not in faeces and urine.The enterohepatic circulation of labelled pregnenolone and corticosterone was studied in a series of rats consisting of five animals connected by cannulae between the bile duct of one rat and the duodenum of the next rat. The average time for an enterohepatic circulation was calculated to be 3—4 h. The ratio between radioactivities eliminated in faeces and urine increased progressively and markedly with each enterohepatic cycle, as did the ratio between conjugated and free steroids. It is concluded that the steroids undergo extensive metabolism in each enterohepatic cycle and that labelled steroids injected into rats are unlikely to be fully mixed with the endogenous pools before being excreted.
Fatty Acid Degradation in Escherichia coli
Authors: Klein Klaus , Steinberg Regina , Fiethen Brigitte , Overath Peter 
Published: March 2005

The properties of a transport system for the uptake of fatty acids into Escherichia coli cells are described. The system is induced under the same conditions as the enzymes involved in fatty acid degradation. In accordance with the chain‐length specificity of the acyl‐CoA synthetase, only fatty acids with more than eight carbon atoms are taken up. The reduced rate of uptake of fatty acids in mutants with various lesions in fatty acid degradation indicates that transport and metabolism are tightly coupled processes. The absence of an efflux reaction and the inability of a mutant lacking the acyl‐CoA synthetase to take up fatty acids support the hypothesis that this enzyme is involved in a vectorial acylation during the permeation process.
Mutants lacking one or all of the enzymes enoyl‐CoA hydrase, β‐hydroxyacyl‐CoA dehydro‐genase and thiolase, when assayed with substrates having four carbon atoms, can partially degrade long‐chain length and medium‐chain length fatty acids. This suggests that there are at least two types of enzyme activity in the cell which differ in their specificities for acyl‐CoA substrates of various chain‐lengths.
A new old locus situated between the genes proA and proB on the E. coli linkage group is described. Lesions in this gene make the cell unable to degrade fatty acids of any carbon number, and must therefore lack an element common to the degradation of all fatty acids. Fatty acids taken up by these mutants are exclusively incorporated into membrane phospholipids.
Induction of Enzymes Involved in the Catabolism of Deoxyribonucleosides and Ribonucleosides in Escherichia coli K 12
Authors: Hammer‐Jespersen Karin , Munch‐Petersen Agnete , Nygaard Per , Schwartz Marianne 
Published: March 2005

When cells of Escherichia coli are grown in the presence of deoxyribonucleosides with glucose or glycerol as carbon sources the following enzymes are induced: deoxyriboaldolase, thymidine phosphorylase, deoxyribomutase, and purine nucleoside phosphorylase. Experiments with mutants deficient in one of the enzymes support the conclusion that formation of deoxyribose‐5‐phosphate is required for this induction.Two of these enzymes, deoxyribomutase and purine nucleoside phosphorylase, are also induced in the presence of purine ribonucleosides. Evidence is presented that in this case phosphorolysis of the added purine nucleosides is not required for induction and, furthermore, that adenosine gives rise to induction only after prior deamination to inosine.Addition of adenosine to glycerol‐grown cells of strains deficient in purine nucleoside phosphorylase, gives rise to an unspecific induction of nucleoside catabolizing enzymes in general.
Subcellular Distribution of Sulfite Cytochrome c Reductase in Rat Liver Tissue
Authors: Wattiaux‐De Coninck Simone , Wattiaux Robert 
Published: March 2005

The intracellular distribution of sulfite cytochrome c reductase was investigated in homogenates of rat liver and compared with the distribution of cytochrome oxidase, acid phosphatase, catalase and glucose‐6‐phosphatase which were used respectively as reference enzymes for mitochondria, lysosomes, peroxisomes and endoplasmic reticulum. 60% of the enzyme is recovered in the mitochondrial fraction, the remainder being found principally in the soluble fraction.The total mitochondrial fraction was analyzed by differential centrifugation in a stabilizing sucrose gradient and by isopycnic centrifugation in a sucrose gradient. The distribution curves of sulfite cytochrome c reductase are similar to those of two mitochondrial enzymes, cytochrome oxidase and adenylate kinase, and quite different from those of reference enzymes of other particles.Sulfite cytochrome c reductase exhibits a structure‐linked latency. The enzyme can be unmasked and solubilized by hypotonic treatment and by digitonin. In the activation experiments, its behaviour was similar to that of adenylate kinase and different from that of glutamate dehydrogenase.These findings are discussed in the light of the results of other authors. It is concluded that most of the rat liver sulfite cytochrome c reductase is associated with the mitochondria and is probably situated in the intermembrane space of these granules.
The Influence of pH and Methylene Blue on the Pathways of Glucose Utilization and Lactate Formation in Erythrocytes of Man
Authors: Albrecht Volker , Roigas Henn , Schultze Maria , Jacobasch Gisela , Rapoport Samuel 
Published: March 2005

The influence of pH on the contributions of the Embden‐Meyerhof and of the oxidative pentose‐phosphate pathways in the utilization of glucose by human erythrocytes in the presence and absence of methylene blue were determined from yields of 14CO2 and [14C]lactate.In the absence of methylene blue both the NADP+ concentration and the phosphofructokinase are controlling factors. At pH 7.0 the oxidative pentose‐phosphate pathway accounts for nearly one‐half of the metabolic flux. Its contribution nearly vanishes at pH 8.2.In the presence of methylene blue the limitation by the NADP+ concentration disappears. At pH values of 7.4 and below the phosphofructokinase is completely inhibited and is circumvented for the formation of lactate. The limitation of the glucose influx resides in the hexokinase. At pH 8.2 both the Embden‐Meyerhof and the oxidative pentose‐phosphate pathway participate in the metabolic flux, since the inhibition of the phosphofructokinase is released.With methylene blue metabolic pools are formed. They are derived exclusively from the oxidative pentose‐phosphate pathway up to pH 7.5–7.6 and entirely from the Embden‐Meyerhof pathway at pH 8.2.
Energy Transfer Inhibition and Ion Movements in Isolated Chloroplasts
Authors: Karlish Steven J. D. , Avron Mordhay 
Published: March 2005

Valinomycin and low concentrations of gramicidin act as energy transfer inhibitors in chloroplasts.
Light‐induced H+ uptake and the H+/e− ratio were stimulated by valinomycin, especially above pH 7.5, while the basal electron transport (–ADP) was inhibited. The maximal H+/e− ratio observed in the presence of valinomycin was 4 (at pH 6.5).
The relationship between light‐induced K+ efflux and proton uptake, both in the presence or absence of valinomycin, is not a stoichiometric one.
Explanations for the observed phenomena, based on the possibility of H+ or K+ binding to fixed negative charges within the thylakoids are discussed.
Methionine Metabolism and Cephalosporin C Synthesis in Cephalosporium acremoniumd‐Amino Acid Oxidase
Authors: Benz F. , Liersch M. , Nüuesch J. , Treichler H. J. 
Published: March 2005

The d‐amino acid oxidase was produced during the growth cycle of Cephalosporium acremo‐nium in submerged culture.The enzyme is strictly sterospecific for d‐amino acids as substrates. It was isolated from the mycelial crude extract and purified 18‐fold. A relatively small number of d‐monoamino acids were deaminated. With d‐methionine as substrate the enzyme had a pH optimum of 8.5 and it was competitively inhibited by the d‐stereoisomers of norleucine, norvaline, leucine, isoleucine, phenylalanine and lysine.The properties of the C. Acremonium enzyme are compared with those of other fungi and mammalian d‐amino acid oxidases. Its possible influence on the biosynthesis of the antibiotic Cephalosporin C is discussed.
Effect of Reduction of the Intestinal Microflora on the Excretion of Neutral Steroids in Human Faeces and Urine
Authors: Jänne Olli A. , Laatikainen Timo J. , Vihko Reijo K. 
Published: March 2005

Neutral steroid glucuronides and mono‐ and disulphates in faeces and urine of normal adult males were analysed before and during phthalylsulphathiazole treatment in order to clarify whether faecal and urinary excretion of C19 and C21 steroids is modified by reduction of the intestinal microflora. For the same purpose, the unconjugated neutral steroids in faeces were analysed, too. During the sulphonamide treatment, the profile of faecal neutral steroid sulphates became very similar to that in bile. The amount of sulphate‐conjugated neutral steroids, especially disulphates, was increased and the pattern of the faecal steroids indicated a decrease in the oxidoreducing and epimerising activities of the intestinal contents. No neutral steroid glucuronides were detected in faeces either before or during the sulphonamide treatment. The urinary excretion of neutral steroid conjugates was very little affected by the administration of the drug. However, most of the 16‐hydroxylated C19 steroid monosulphates were excreted in urine in larger amounts during the treatment than before it.The results obtained indicate that in normal adult subjects changes in the composition of the intestinal microflora greatly modify faecal steroid excretion, but seem to be of very little importance for the urinary output of a large number of neutral steroid conjugates.
Resolution of Nitrogenase of Mycobacterium flavum 301 into Two Components and Cross Reaction with Nitrogenase Components from Other Bacteria
Authors: Biggins David R. , Kelly Michael , Postgate John R. 
Published: March 2005

Nitrogenase from the aerobe Mycobacterium flavum 301 was resolved into two protein fractions resembling those obtained from other nitrogen‐fixing bacteria as regards reduction of N2, C2,H2, cyanide and methyl isocyanide. Fraction 1 contained iron and molybdenum (about 9:1); fraction 2 contained iron only, was rapidly inactivated by oxygen and was cold‐labile. Neither fraction was detected in ammonia‐grown organisms.
The optimum ratio of fraction 1 to fraction 2 for acetylene reduction was about 3:1; that for cyanide or methyl isocyanide was greater than 6.5:1.
Fractions from M. flavum 301 reduced acetylene in combination with nitrogenase fractions from Bacillus polymyxa, Klebsiella pneumoniae and Rhodospirillum rubrum, weakly with Azotobacter chroococcum, not at all with Clostridium pasteurianum.

Fraction 1 from R. rubrum, reduced acetylene with fraction 2 from M. flavum 301, K. pneumonie, B. polymyxa and A. chroococcum, but not C. pasteurianum.
Isolation of the Human Retinol Binding Protein by Affinity Chromatography
Authors: Vahlquist Anders , Nilsson Sten F. , Peterson Per A. 
Published: March 2005

The human retinol binding protein, which in plasma is bound to thyroxine binding prealbumin, has been isolated in free form from urine of patients with tubular proteinuria and from normal serum. The isolation procedure for urinary retionl binding protein involved gel chromatography and affinity chromatography on a column of prealbumin coupled to Sepharose, whereas the isolation of serum retinol binding protein required three fractionation steps; DEAE‐Sephadex chromatography, and affinity chromatography.The retinol binding protein from urine and serum was obtained in a yield of 31% and 42% respectively. The relatively low yield of the urinary protein was explained by the fact that two forms of retinol binding protein were present in the urine, one of which did not bind to prealbumin. The purity of the retinol binding protein isolated from urine and serum was established by the following criteria: immunoelectrophoresis, polyacrylamide gel electrophoresis, amino acid analyses, and sedimentation equilibrium ultracentrifugations.The use of affinity chromatography offers a simple and rapid procedure for the isolation of moderate quantities of highly purified retinol binding protein from urine and serum.
The Subunit Structure of the Escherichia coli K‐12 Pyruvate Dehydrogenase Complex
Authors: Vogel Otto , Beikirch Helga , Müller Harald , Henning Ulf 
Published: March 2005

The dihydrolipoamide transacetylase component of the Escherichia coli K‐12 pyruvate dehydrogenase complex has been shown to consist of identical or very nearly identical polypeptide chains with a molecular weight of 80 000 (± 5%).Amino acid and tryptic peptide analyses gave a minimum chemical molecular weight of about 80 000. Carboxypeptidase degradation revealed one C‐terminal sequence …Arg‐Arg‐(Val,Leu)‐Met‐CO2H per 80 000 molecular weight protein. An N‐terminal amino acid was not found. Dodecylsulfate polyacrylamide gel electrophoresis of the transacetylase subunit (either native, performic acid oxidized, or carboxymethylated) showed one protein band moving as a species with molecular weight of 80 000.These data are at variance with the results of Reed and associates who had found that the transacetylase component of the E. coli Crookes pyruvate dehydrogenase complex consists of identical 36000 molecular weight polypeptide chains. It has been found that in strain W945 T1 of E. coli K‐12, the 80 000 molecular weight transacetylase subunit is cleaved during the purification procedure, yielding a major fragment with a molecular weight of about 38000. It is possible that this cleavage explains the inconsistency between the transacetylase subunit molecular weights.It has been confirmed that the dihydrolipoamide dehydrogenase consists of subunits with molecular weight 56000.A new, relatively rapid purification procedure for the pyruvate dehydrogenase complex is described; it allows the preparation of 200–300 mg enzyme complex, more than 90% pure, within one week.
The pH6 Acetolactate‐Forming Enzyme from Aerobacter aerogenes Subunit Structure
Authors: Huseby Nils‐Erik , Christensen Terje B. , Olsen Bjørn Reino , Størmer Fredrik C. 
Published: March 2005

The native and subunit molecular weights of the pH6 acetolactate‐forming enzyme from Aerobacter aerogenes have been investigated by sedimentation equilibrium analysis and gel electrophoresis. The values obtained are 220 000 for the native enzyme and 58 000 for its subunits. The native enzyme is dissociated into four equal‐sized subunits by exposure to guanidine hydrochloride, urea, or sodium dodecylsulfate.Electron micrographs of enzyme molecules, negatively stained, show that they appear as spherical particles with a diameter of about 6 nm forming dimeric structures of two particles close together. The molecular weight as calculated from the diameter of the particles, are consistent with the values obtained by sedimentation equilibrium and gel electrophoresis. The native enzyme molecule is visualized as a morphological dimer with each particle containing two polypeptide chains of similar size.
Structure primaire de la caséine β bovine
Authors: Ribadeau‐dumas Bruno , Brignon Ghislaine , Grosclaude François , Mercier Jean‐Claude 
Published: March 2005

All the expected tryptic and CNBr peptides from bovine β‐casein A2 were previously isolated and analyzed [1]. The complete positioning of these peptides was reported later on [2].The present report deals with the sequencing of 65 amino acid residues at the carboxyl‐terminus of β‐casein A2: ‐His‐Gln‐Pro‐His‐Gln‐Pro‐Leu‐Pro‐Pro‐Thr‐Val‐Met‐Phe‐Pro‐Pro‐Gln‐Ser‐Val‐Leu‐ Ser‐Leu‐Ser‐Gln‐Ser‐Lys‐Val‐Leu‐Pro‐Val‐Pro‐Glu‐Lys‐Ala‐Val‐Pro‐Tyr‐Pro‐Gln‐Agr‐Asp‐Met‐Pro‐Ile‐Gln‐Ala‐Phe‐Leu‐Leu‐Tyr‐Gln‐Gln‐Pro‐Val‐Leu‐Gly‐Pro‐Val‐Arg‐Gly‐Pro‐Phe‐Pro‐Ile‐Ile‐Val · OH.This result was obtained by using well known methods such as enzymic or chemical cleavages of the peptide chain, fractionation of peptides by Sephadex or Dowex column chromatography, paper electrophoresis or chromatography, and sequential Edman degradation.The carboxyl‐terminal tryptic peptide is very likely identical with a peptide isolated by Matoba et al. [3] from a tryptic digest of whole casein, and characterized by its bitter taste.
Structure primaire de la caséine β bovine
Authors: Ribadeau dumas Bruno , Brignon Ghislaine , Grosclaude François , Mercier Jean‐Claude 
Published: March 2005

In previous work from this laboratory, all the expected tryptic and CNBr peptides of the bovine β‐casein A2 were isolated, analyzed and positioned in the peptide chain [1,2]. The sequence of 65 residues from the carboxyl‐terminus of this casein was also given [3].In this communication we report the sequence of 32 residues from the amino‐terminus: H · Arg‐Glu‐Leu‐Glu‐Glu‐Leu‐Asn‐Val‐Pro‐Gly‐Glu‐Ile‐Val‐Glu‐SerP‐Leu‐SerP‐Serp‐Serp‐Glu‐Glu‐Ser‐Ile‐Thr‐Arg‐Ile‐Asn‐Lys‐Lys‐Ile‐Glu‐Lys.This result was obtained by using, as starting material, β‐A2 tryptic peptides T1, T9 and T11 [1], whose alignment, H.T1‐T9‐T11, was previously established [2].The amino‐acid sequence of the phosphopeptide T1 was determined mainly from fragments resulting of hydrolysis by thermolysin.This very acidic peptide contains 4 of the 5 phosphorus atoms of β‐casein A2, 5 seryl and 1 threonyl residues. The 5 seryl residues were obtained in a single peptide resulting of hydrolysis by thermolysin. This peptide (T1Th1) contains 4 phosphorus atoms that can be readily removed by an ortho‐phosphoric monoester phosphohydrolase. Thus it can be inferred that T1 contains 4 phosphoseryl and 1 free seryl residues. The position of the different seryl residues was deduced from analysis of T1, T1Th1 and of dephospho‐T1Th1. The only threonyl residue of T1 is not phosphorylated.Since five seryl residues were found in peptide T1, instead of the four previously mentioned, the total number of residues in β‐casein A2 amounts to 209 instead of 208 [1–3].The sequence given above for T1 is very similar to the one recently reported by Manson [4].
Conformational Changes in a Synthetic Antigen Induced by Specific Antibodies
Authors: Schechter Bilha , Conway‐jacobs Abigail , Sela Michael 
Published: March 2005

The high molecular weight copolymer (mol. wt. = 75 000) containing the repeating sequence–(l‐Tyr‐l‐Ala‐l‐Glu)–and denoted as polypeptide (Tyr‐Ala‐Glu)n has previously been shown to possess an α‐helical structure under physiological conditions. Studies were performed to check whether monovalent fragments of antibodies derived from anti‐(Tyr‐Ala‐Glu)n antibodies could convert the partially helical oligopeptide (Tyr‐Ala‐Glu)13 into a more helical conformation.Circular dichroic spectra of mixtures of the monovalent antibody fragments with (Tyr‐Ala‐Glu)13 were measured at two different concentrations of both components. Analogous experiments were done with the same fragments and the polypeptide (Tyr‐Ala‐Glu)n. When anti‐(Tyr‐Ala‐Glu)n antibody fragments were mixed with (Tyr‐Ala‐Glu)13. When the same fragments were mixed with the polypeptide (Tyr‐Ala‐Glu)n, a difference spectrum was observed at the ellipticity band of the polypeptide centered at 275 nm. It was concluded that anti‐(Tyr‐Ala‐Glu)n monovalent antibody fragments could not only convert the (Tyr‐Ala‐Glu)13 into a structure more similar to the polypeptide (Tyr‐Ala‐Glu)n, but could also stabilize the helical content of this polypeptide.
Kinetics of the Inhibition of Aspartate Aminotransferase Isozymes by dl‐Glyceraldehyde 3‐Phosphate
Authors: Kopelovich Levy , Sweetman Lawrence , Nisselbaum Jerome S. 
Published: March 2005

The inhibitor dissociation constants and types of inhibition of the isozymes of aspartate aminotransferase from rat liver by the time‐dependent inhibitor dl‐glyceraldehyde 3‐phosphate were determined from residual enzyme activity after equilibration of each isozyme with the inhibitor and one substrate in the preliminary incubation mixtures.The results showed that the inhibition of the cationic isozyme was completely competitive with respect to α‐ketoglutarate and completely noncompetitive with respect to l‐aspartate. The pyridoxamine form of the cationic isozyme was approximately 10 times more sensitive to inhibition by dl‐glyceraldehyde 3‐phosphate (Ki= 0.084 mM) than the pyridoxal form (Ki= 0.98 mM). Inhibition of the anionic isozyme was mixed partially competitive‐partially noncompetitive with respect to α‐ketoglutarate and partially noncompetitive with respect to l‐aspartate. The pyridoxamine form of the anionic isozyme was approximately 5 times more sensitive to inhibition by dlDL‐glyceraldehyde 3‐phosphate (Ki= 0.39 mM) than the pyridoxal form (Ki= 1.9 mM). Both forms of the cationic isozyme were more sensitive to inhibition than the corresponding forms of the anionic isozyme.The degree to which inhibition of the anionic isozyme was partial was assessed by determining the interaction constants α and β. These were α= 6.9 and β= 0.32, and indicated that the anionic isozyme, when fully combined with dl‐glyceraldehyde 3‐phosphate, retained 32% of its catalytic capacity. The cationic isozyme was completely inhibited with α=∞ and β= 0.Comparison of the Ki values for the pyridoxamine and pyridoxal forms of the isozymes of aspartate aminotransferase with the concentrations of d‐glyceraldehyde 3‐phosphate reported for perfused liver and for incubated erythrocytes suggests that inhibition may occur in vivo.
Correlation Between H+ and Anion Movement in Mitochondria and the Key Role of the Phosphate Carrier
Authors: Mcgivan John D. , Klingenberg Martin 
Published: March 2005

The mechanism according to which anions such as di‐ and tricarboxylates are accumulated in mitochondria are investigated with respect to H+ movement and the role of the Pi carrier.

In the absence of respiration, malate is taken up mainly by net accumulation with H+/malate = 1.6. When corrected for exchange with Pi, H+/malate = 2 is found. Under aerobic conditions malate is taken up mainlay in exchange for Pi. The ratio H+/malate is largely independent of the pH despite strong pH dependence of the malate uptake.
The citrate/malate exchange is neutralized by the movement of 1 H+ in the direction of both citrate uptake or efflux.
The net uptake of malate and citrate is abolished by SH reagents demonstrating a key role of the Pi carrier in the net accumulation of di‐ and tricarboxylates.
The uptake of malate and citrate is increased by respiration. This increase is also dependent on the function of the Pi carrier.
For the movement of Pi a ratio H+/Pi= 1.5 at pH 6.9 is obtained, in fair agreement with a theoretical H+/Pi at pH =pK of the dissociation of Pi‐ to Pi2‐.
Anion distribution not coupled to the Pi carrier, such as the distribution of glutamate, is not linked to H+ movement and to energy‐linked accumulation.
The role of the H+ gradient and of energy coupling via the Pi carrier in maintaining different redox potentials across the inner mitochondrial membrane is discussed.
Crystallographic Evidence for the Tetrameric Subunit Structure of l‐Asparaginase from Escherichia coli
Authors: Epp Otto , Steigemann Wolfgang , Formanek Helmut , Huber Robert 
Published: March 2005

The analysis of a monoclinic crystal modification of l‐asparaginase from Escherichia coli supports the chemical and physio‐chemical evidence for a tetrameric subunit structure.The pseudo‐symmetries occurring in the crystal structure provide evidence that the molecules lie on positions with approximate point symmetry 222.