The effect of glucose and ammonium sulfate on kinetic acidification by heterogeneous mixed culture

Summary The effect of glucose and ammonium sulfate concentration on the kinetics of lactic acid formation by a heterogeneous mixed culture was evaluated by the sole product formation using the Gompertz model, which can be used to define culture media composition taking into account product accumulation and acidification rate constant. A compromise between ionic inhibition and nitrogen limitation was found by using ammonium sulfate as nitrogen source. The sugar tolerance was similar to that in exenic cultures.     

Regulation of reduced nitrogen assimilation in Rhodobacter capsulatus E1F1

The phototrophic bacterium Rhodobacter capsulatus E1F1 assimilates ammonia and other forms of reduced nitrogen either through the GS/GOGAT pathway or by the concerted action of l-alanine dehydrogenase and aminotransferases. These routes are light-independent and very responsive to the carbon and nitrogen sources used for cell growth. GS was most active in cells grown on nitrate or l-glutamate as nitrogen sources, whereas it was heavily adenylylated and siginificantly repressed by ammonium, glycine, l-alanine, l-aspartate, l-asparagine and l-glutamine, under which conditions specific aminotransferases were induced. GOGAT activity was kept at constitutive levels in cells grown on l-amino acids as nitrogen sources except on l-glutamine where it was significantly induced during the early phase of growth. In vitro, GOGAT activity was strongly inhibited by l-tyrosine and NADPH. In cells using l-asparagine or l-aspartate as nitrogen source, a concerted induction of l-aspartate aminotransferase and l-asparaginase was observed. Enzyme level enhancements in response to nitrogen source variation involved de novo protein synthesis and strongly correlated with the cell growth phase.Abbreviations ADH l-alanine dehydrogenase - AOAT l-alanine:2-oxoglutarate aminotransferase - Asnase l-asparaginase - GOAT Glycine: oxaloacetate aminotransferase - GOGAT Glutamate synthase - GOT l-aspartate: 2-oxoglutarate aminotransferase - GS Glutamine synthetase - HPLC High-Pressure Liquid Chromatography - MOPS 2-(N-morpholino)propanesulfonic acid - MSX l-methionine-d,l-sulfoximine     

Immunocytochemical study of parvalbumin fibers and cell bodies in the rat hipothalamus

The distribution of parvalbumin (PA) cell bodies and fibers in the hypothalamus of the rat was studied using a monoclonal antibody and the avidin-biotin-peroxidase method. The densest clusters of immunoreactive perikarya were observed in the nuclei mamillare medialis, arcuatus and dorsomedialis hypothalami, whereas the corpus mamillare lateralis had the lowest density. The densest network of immunoreactive fibers was observed in the corpus mamillare lateralis and nucleus arcuatus. The corpus mamillare medialis contained a moderate number of PA fibers, whereas the nucleus dorsomedialis hypothalami had the lowest density of immunoreactive fibers. In addition, a large number of immunoreactive fibers was found in the tractus opticus and the tractus mamillo-thalamicus. Essentially, the distribution of PA in the rat hypothalamus after using a monoclonal antibody seems to be broader in comparison with previous studies carried out in the same diencephalic region of the rat. The presence of PA in several nuclei of the rat hypothalamus suggests that this protein could be directly or indirectly involved in neuroendocrine, limbic and visual functions.     

The epsilon-subunit of ATP synthase from bovine heart mitochondria. Complementary DNA sequence, expression in bovine tissues and evidence of homologous sequences in man and rat.

The epsilon-subunit of ATP synthase from bovine heart mitochondria is assembled into the extrinsic membrane sector, F1-ATPase. The mature protein is 50 amino acid residues in length and its function is unknown. It is a nuclear gene product that is imported into the organelle. A mixture of 64 oligonucleotides 17 bases long, designed on the basis of the known protein sequence, was synthesized and used as a hybridization probe to isolate a cognate cDNA clone from a bovine library. The DNA sequence of this clone was determined, and the protein sequence of the epsilon-subunit deduced from it agrees exactly with that determined by direct sequence analysis of the protein isolated from bovine hearts. The bovine cDNA was used as a hybridization probe to examine the expression of the epsilon-subunit in various bovine tissues. mRNAs related to the cDNA are found in all of these tissues, and no evidence was obtained of the presence of mRNAs for the epsilon-subunit with similar coding sequences and dissimilar 3' non-coding regions. By hybridization experiments with digests of DNA from cow, man and rat it has been shown that sequences related to the bovine cDNA are present in the genomes of all three species. More than one related sequence was detected in all cases, indicating the presence in all three genomes of more than one gene and/or pseudogenes.     

Dicarboxylic acid anhydrides as dissociating agents of protein-containing structures

Dissociation of protein-containing structures by modification of protein amino groups with dicarboxylic acid anhydrides is a mild procedure which, in some cases, offers advantages over treatment with alternative dissociating agents, such as urea, guanidine hydrochloride, detergents, high ionic strength, and extremes of pH: In addition to dissociating multimeric proteins and protein aggregates, dicarboxylic acid anhydrides are effective dissociating agents for membrane-bound proteins and nucleoprotein particles. With most dicarboxylic acid anhydrides reviewed, the introduced reagent residues can be eliminated under moderate acid conditions, which allows the purification of unmodified individual components, and the use of disassembly-reconstitution systems valuable for investigating the structural and functional roles played by the individual components of complex particles:Each reagent can be suitable for a particular purpose, depending on the required specificity of the modification and stability of the modified groups: The stability of the acylated amino groups ranges from the very stable succinylated amino groups to the very labile acylation obtained with dimethylmaleic anhydride: Between these extremes, the stability of the modified amino groups decreases stepwise in the following order: maleic, exo-cis-3,6-endoxo-⁴-tetrahydrophthalic, citraconic, and 3,4,5,6-tetrahydrophthalic anhydride. With respect to the selectivity of the produced modification, little or no modification of hydroxyamino acid and cysteine residues has been observed with dimethylmaleic, exo-cis-3,6-endoxo-⁴-tetrahydrophthalic, and 3,4,5,6-tetrahydrophthalic anhydrides: With the other reagents, the extent of modification of hydroxyamino acid residues increases in the order citraconic, maleic and succinic anhydride: Citraconic and maleic anhydrides can produce irreversible modification of cysteine residues, the reactivity of sulfhydryl groups being higher with maleic anhydride:     

Influence of the solvent on the conformational-dependent properties of random coil polypeptides. II. Mean square optical anisotropies and Kerr constants

Mean square optical anisotropies and molar Kerr constants were calculated for homopolypeptides of the 20 natural amino acids and of several enzymes and proteins in the random-coil state. The effect of hydration was taken into account in constructing the molecular potential that gives the conformational energies as a function of the rotational angles phi and psi of the backbone and chi(1) of the side chain. The Rotational Isomeric State model was used in calculated energies, the Valence Optical Scheme and the matrix calculus technique of Flory being employed in the evaluation of the optical properties. The results are compared with calculations for the same substances that were performed without taking into account the solvent, as well as with other similar studies. The Kerr constant is confirmed as being one of the most sensitive properties of a given polypeptide to the residue class and to the sequence of those residues.     

Metabolic adaptation of the renal carbohydrate metabolism. I. Effects of starvation on the gluconeogenic and glycolytic fluxes in the proximal and distal renal tubules

Summary The influence of starvation on renal carbohydrate metabolism was studied in the proximal and distal fragments of the nephron. Starvation induced a double and opposite adaptation mechanism in both fractions of the renal tubule. In renal proximal tubules, the gluconeogenic flux was stimulated progressively during a period of 48 hours of starvation (2.15 fold), due, in part, to a significant increase in the fructose 1,6-bisphosphatase and phosphoenolpyruvate carboxykinase activities although with different characteristics. Fructose 1,6-bisphosphatase activity from this tubular fragment increased only at subsaturating subtrate concentration (68%) which involved a significant decrease in the Km (35%) for fructose 1,6-bisphosphate while there was no change in Vmax. This behaviour clearly indicates that it is related to modifications in the activity of the preexistent enzyme in the cell. Proximal phosphoenolpyruvate carboxykinase activity increased proportionally at both substrate concentrations (86 and 89% respectively) which brought about changes in Vmax without changes in Kin, all of which are in accordance with variations in the cellular levels of the enzyme. In the renal distal tubules, the glycolytic capacity drastically decreased throughout the starvation time. At 48 hours 65% of inhibition was shown. We have found a short term regulation of phosphofructokinase activity by starvation which involves an increase in Km (2.2 fold) without changes in Vmax, as a result of these kinetic changes, an inactivation of phosphofructokinase was detected at subsaturating concentration of fructose 6-phosphate. On the contrary, this nutritional state did not modify the kinetic behaviour of renal pyruvate kinase. Finally, neither proximal glycolytic nor distal gluconeogenic capacities and related enzymes activities were changed during starvation.     

Degradation of diarylethane structures by Pseudomonas fluorescens biovar I

Pseudomonas fluorescens biovar I was isolated from a pulp mill effluent based on its ability to grow on synthetic media containing 1,2-diarylethane structures as the sole carbon and energy source. Analysis of samples taken from cultures of this strain in benzoin or 4,4-dimethoxybenzoin (anisoin), showed that cleavage between the two aliphatic carbons takes place prior to ring fission. Intermonomeric cleavage was also obtained with crude extracts. Substrates of this reaction were only those 1,2-diarylethane compounds that supported growth of the bacterium. The purification and partial characterization of an enzyme that catalyzes the NADH-dependent reduction of the carbonyl group of benzoin and anisoin is also reported.     

Regional brain GABA metabolism and release during hepatic coma produced in rats chronically treated with carbon tetrachloride

Hepatic coma was induced in rats chronically treated with CCl₄, by means of a single injection of ammonium acetate. The activities of glutamate decarboxylase (GAD) and GABA transaminase (GABA-T), as well as the synaptosomal uptake and release of [³H]GABA, were measured in the following brain areas of the comatose rats: cortex, striatum, hypothalamus, hippocampus, midbrain and cerebellum. Hepatic coma was associated with a general decrease of GAD activity, whereas GABA-T activity was diminished only in the hypothalamus, striatum and midbrain. During hepatic coma, the K⁺-stimulated [³H]GABA release was notably diminished in the striatum and cerebellum, whereas a significant increase was observed in the hippocampus. [³H]GABA uptake increased in most regions after CCl₄ treatment, independently of the presence of coma. The results indicate that GABAergic transmission seems to be decreased in most cerebral regions during hepatic coma.