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PubMed1979

Concerted repression of the synthesis of the arginine biosynthetic enzymes by aminoacids: a comparison between the regulatory mechanisms controlling aminoacid biosyntheses in bacteria and in yeast.

It has been shown that in bacteria, besides specific regulatory mechanisms, the synthesis of aminoacid biosynthetic enzymes is also controlled by the endogenous aminoacid pool. The latter regulates the intracellular level of ppGpp, a positive effector of RNA messenger transcription. A similar regulatory control exists in yeast but does not appear to involve the same general effector. This was established by the observation that derepression of the enzymes belonging to several aminoacid biosynthetic pathways follows aminoacid starvation or tRNA discharging. We now report the repression of the arginine pathway by the total aminoacid pool. New mutations affecting the repressibility of the arginine enzymes as well as enzymes belonging to other aminoacid biosyntheses, when cells are grown in the presence of an excess of aminoacids, were identified.

Amino Acids↗
PubMed1997

The relative phospholamban and SERCA2 ratio: a critical determinant of myocardial contractility.

Phospholamban is a regulatory phosphoprotein which modulates the active transport of Ca2+ by the cardiac sarcoplasmic reticular Ca(2+)-ATPase enzyme (SERCA2) into the lumen of the sarcoplasmic reticulum. Phospholamban, which is a reversible inhibitor of SERCA2, represses the enzyme's activity, and this inhibition is relieved upon phosphorylation of phospholamban in response to beta-adrenergic stimulation. In this way, phospholamban is an important regulator of SERCA2-mediated myocardial relaxation during diastole. This report centers on the hypothesis that the relative levels of phospholamban: SERCA2 in cardiac muscle plays an important role in the muscle's overall contractility status. This hypothesis was tested by comparing the contractile parameters of: a) murine atrial and ventricular muscles, which differentially express phospholamban, and b) murine wild-type and phospholamban knock-out hearts. These comparisons revealed that atrial muscles, which have a 4.2-fold lower phospholamban: SERCA2 ratio than ventricular muscles, exhibited rates of force development and relaxation of tension, which were three-fold faster that these parameters for ventricular muscles. Similar comparisons were made via analyses of left-ventricular pressure development recorded for isolated, work-performing hearts from wild-type and phospholamban knock-out mice. In these studies, hearts from phospholamban knock-out mice, which were devoid of phospholamban, exhibited enhanced parameters of left-ventricular contractility in comparison to wild-type hearts. These results suggest that the relative phospholamban: SERCA2 ratio is critical in the regulation of myocardial contractility and alterations in this ratio may contribute to the functional deterioration observed during heart failure.

Animals↗
PubMed2005

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) degradation by Acetobacterium paludosum.

Substrates and nutrients are often added to contaminated soil or groundwater to enhance bioremediation. Nevertheless, this practice may be counterproductive in some cases where nutrient addition might relieve selective pressure for pollutant biodegradation. Batch experiments with a homoacetogenic pure culture of Acetobacterium paludosum showed that anaerobic RDX degradation is the fastest when auxiliary growth substrates (yeast extract plus fructose) and nitrogen sources (ammonium) are not added. This bacterium degraded RDX faster under autotrophic (H2-fed) than under heterotrophic conditions, even though heterotrophic growth was faster. The inhibitory effect of ammonium is postulated to be due to the repression of enzymes that initiate RDX degradation by reducing its nitro groups, based on the known fact that ammonia represses nitrate and nitrite reductases. This observation suggests that the absence of easily assimilated nitrogen sources, such as ammonium, enhances RDX degradation. Although specific end products of RDX degradation were not determined, the production of nitrous oxide (N2O) suggests that A. paludosum cleaved the triazine ring.

Acetobacterium↗
PubMed1992

Loss of peroxisomal enzyme expression in preneoplastic and neoplastic lesions induced by peroxisome proliferators in rat livers.

Immunohistochemical staining of enoyl CoA hydratase (ECH), a key peroxisomal enzyme, revealed that the putative preneoplastic lesions induced in livers by administration of the peroxisome proliferator (PP) clofibrate (0.3% in diet) to rats for 60 weeks or more, lacked this enzyme so that they could be detected as ECH-negative foci. ECH and other peroxisomal enzymes such as acyl CoA oxidase, catalase and carnitine-dependent acetyltransferase were also either not or only weakly expressed in most hepatic hyperplastic nodules and hepatomas induced by ciprofibrate (0.025% in diet), Wy-14,643 (0.1%) or BR-931 (0.2%), while being strongly induced in surrounding hepatocytes. These results indicate that the expression of ECH and other peroxisomal enzymes is repressed in putative preneoplastic and neoplastic lesions induced by PPs in rat livers and that these peroxisomal enzymes might therefore be used as negative markers.

Animals↗
PubMed1980

Regulation of carbamylphosphate synthesis in Serratia marcescens.

Serratia marcescens HY possessed a single carbamylphosphate synthase (CPSase) which was subject to cumulative repression by arginine and a pyrimidine. CPSase did not appear to be a part of a multifunctional enzyme complex as is the case for other enzymes of pyrimidine biosynthesis in this organism. CPSase was purified to homogeneity. The molecular weight of the enzyme was estimated to be 167,000 by sucrose density gradient ultracentrifugation. The double-reciprocal plot for magnesium adenosine triphosphate was linear, yielding a Km value of 2.5 mM. The enzyme utilized either glutamine (Km, 0.1 mM) or NH3 (Km, 10.5 mM) as a nitrogen donor in the reaction. CPSase activity was subject to activation by ornithine and feedback inhibition by uridine monophosphate, as is the case for other enteric bacteria. Carbamate kinase activity, detected in crude extracts of S. marcescens, was shown to be due to a constitutive acetate kinase. The absence of carbamate kinase from S. marcescens HY is consistent with the inability of this organism to utilize arginine as a source of energy under anaerobic conditions.

Adenosine Triphosphate↗
PubMed1981

Immunochemical studies on catabolite inactivation of phosphoenolpyruvate carboxykinase in Saccharomyces cerevisiae.

Phosphoenolpyruvate carboxykinase (EC 4.1.1.49) from Saccharomyces cerevisiae was purified to homogeneity. The enzyme is composed of four subunits of Mr = 64,000. Specific antibodies against phosphoenolpyruvate carboxykinase were raised in rabbits and purified by affinity chromatography. Phosphoenolpyruvate carboxykinase is rapidly inactivated when glucose is added to cells starved for carbon (Haarasilta, S., and Oura, E. (1975) Eur. J. Biochem. 52, 1-7; Gancedo, C., and Schwerzmann, K. (1976)( ARch. Microbiol. 109, 221-225). In the present study this inactivation has been analyzed by immunochemical techniques. It was found that the loss of catalytic activity is paralleled by a decrease in cross-reacting material which suggests degradation of the enzyme. In the absence of glucose the enzyme is degraded very slowly, which indicates that glucose-induced inactivation cannot simply be due to repression of enzyme synthesis in the presence of a rapid rate of degradation. Experiments with a proteinase-deficient mutant showed that proteinase B, carboxypeptidase Y, and carboxypeptidase S are not involved in the inactivation system.

Antibodies↗
PubMed2004

Pyrimidine nucleotide synthesis in Pseudomonas citronellolis.

Pyrimidine biosynthesis was active in Pseudomonas citronellolis ATCC 13674 and appeared to be regulated by pyrimidines. When wild-type cells were grown on succinate in the presence of uracil, the de novo enzyme activities were depressed while only four enzyme activities were depressed in the glucose-grown cells. On either carbon source, orotic acid-grown cells had diminished aspartate transcarbamoylase, dihydroorotase or OMP decarboxylase activity. Pyrimidine limitation of glucose-grown pyrimidine auxotrophic cells resulted in de novo enzyme activities, except for transcarbamoyolase activity, that were elevated by more than 5-fold compared to their activities in uracil-grown cells. Since pyrimidine limitation of succinate-grown mutant cells produced less enzyme derepression, catabolite repression appeared to be a factor. At the level of enzyme activity, aspartate transcarbamoylase activity in P. citronellolis was strongly inhibited by all effectors tested. Compared to the regulation of pyrimidine biosynthesis in taxonomically-related species, pyrimidine biosynthesis in P. citronellolis appeared more highly regulated.

Aspartate Carbamoyltransferase↗
PubMed1976

Repression of Escherichia coli carbamoylphosphate synthase: relationships with enzyme synthesis in the arginine and pyrimidine pathways.

Cumulative repression of Escherichia coli carbamoylphosphate synthase (CPSase; EC 2.7.2.9) by arginine and pyrimidine was analyzed in relation to control enzyme synthesis in the arginine and pyrimidine pathways. The expression of carA and carB, the adjacent genes that specify the two subunits of the enzyme, was estimated by means of an in vitro complementation assay. The synthesis of each gene product was found to be under repression control. Coordinate expression of the two genes was observed under most conditions investigated. They might thus form an operon. The preparation of strains blocked in the degradation of cytidine and harboring leaky mutations affecting several steps of pyrimidine nucleotide synthesis made it possible to distinguish between the effects of cytidine and uridine compounds in the repression of the pyrimidine pathway enzymes. The data obtained suggest that derivatives of both cytidine and uridine participate in the repression of CPSase. In addition, repression of CPSase by arginine did not appear to occur unless pyrimidines were present at a significant intracellular concentration. This observation, together with our previous report that argR mutations impair the cumulative repression of CPSase, suggests that this control is mediated through the concerted effects of regulatory elements specific for the arginine and pyrimidine pathways.

Arginine↗
PubMed2002

Multiple operons connected with catabolism of aromatic compounds in Acinetobacter sp. strain ADP1 are under carbon catabolite repression.

Repression of enzymes contributing to degradation of aromatic compounds via the beta-ketoadipate pathway in the presence of additional carbon sources (carbon catabolite repression) in the bacterium Acinetobacter sp. strain ADP1 is described. The phenomenon was investigated on the level of specific activity of protocatechuate 3,4-dioxygenase and p-hydroxybenzoate hydroxylase participating in catabolism of protocatechuate and p-hydroxybenzoate. Strong repression (90%) was found in cells grown on succinate and acetate in addition to the aromatic carbon source; partial derepression occurred towards the end of the logarithmic growth phase. Glucose, pyruvate, or lactate as secondary carbon sources had no repressing effect. The consumption of the aromatic substrate from the medium was delayed in the presence of acetate and succinate. The differences in specific enzyme activities were reflected at the transcript level for three operons connected to catabolism of aromatic compounds (pob, pca, van) as shown by Northern blot hybridization. Transcriptional fusions between the promoters of the pob and the pca operon identified the transcriptional level as the regulatory one. A mechanism of global regulation is postulated, which enables the organism to consume the offered carbon sources hierarchically in the most efficient manner.

Acinetobacter↗
PubMed1983

The repressible metabolism of sorbitol (D-glucitol) by intact cells of the oral plaque-forming bacterium Streptococcus mutans.

Sorbitol metabolism of Streptococcus mutans was studied. Cocci adapted to growth in sorbitol, glucose or both were challenged to grow on and to ferment those carbohydrates in pH-controlled defined media with intact cells capable of metabolic inductions and regulations. Glucose degradation when in high concentration did not depend upon induction of glucose-specific phosphoenolpyruvate-dependent phosphotransferase activity, as it did at low glucose concentrations. Sorbitol utilization was signalled by the induction of sorbitol-specific phosphoenolpyruvate-dependent phosphotransferase and sorbitol-6-phosphate dehydrogenase activities which persisted throughout the growth cycle. However, when even low levels of glucose were present, sorbitol transport and catabolic activities were rapidly repressed and they were not de-repressed until essentially all glucose had been utilized. Metabolism of sorbitol thus relies on the sorbitol phosphotransferase/sorbitol-6-phosphate dehydrogenase pathway whose activity is sensitively repressed in the presence of glucose.

Enzyme Repression↗