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PubMedDate not supplied

[Use of catabolic repression in the selection of the glucoamylase-producer Aspergillus niger].

The effect of various carbon sources and cAMP on the glucoamylase synthesis in Aspergillus niger was studied to find carbon sources repressed the enzyme synthesis and conditions for the selection of catabolite stable mutants. Maltose at a concentration of 0.5% stimulated the glucoamylase synthesis, but at a concentration of 4% it repressed not only the enzyme synthesis but the growth of the parental strain on the agar medium. The more active mutant 66 was obtained as a result of treatment of Asp. niger st 6 with NG. This mutant is able to grow on the Czapek's medium containing maltose at concentrations 4 or 6%. The mutant 66 produced about 2.9 times more glucoamylase than its parent when maltose was added at 0.5% concentration to the medium. The glucoamylase synthesis in the parental strain was completely repressed under repressing conditions, while the level of the mutant strain activity was 35% from the level of enzyme activity on the medium without the repressor. The addition of cAMP (5.10(-5] resulted in a partial release of maltose (4%) repression of the glucoamylase synthesis in both strains. The results obtained indicate a possibility to select Asp niger mutants with the partially derepressed glucoamylase synthesis. Other regulation mechanisms in addition to catabolite repression may be involved in the regulation of the glucoamylase synthesis.

Aspergillus niger↗
PubMed2002

Reduction in cytochrome P-450 enzyme expression is associated with repression of CAR (constitutive androstane receptor) and PXR (pregnane X receptor) in mouse liver during the acute phase response.

Expression of P-450 (Cyp) enzymes is reduced in liver during the acute phase response, contributing to the decrease in bile acid levels and drug metabolism during infection. Nuclear hormone receptors CAR and PXR are key transactivators of Cyp2b and Cyp3a genes, respectively. Injection of bacterial lipopolysaccharide (LPS) induced the expected reduction in Cyp2b10 and Cyp3a mRNA levels in mouse liver. These decreases were associated with a marked reduction in CAR and PXR mRNA levels within 4 h following treatment. LPS-induced CAR and PXR repression were dose-dependent and sustained for at least 16 h. LPS treatment also reversed the up-regulation of Cyp3a in mice pre-treated with PXR ligand RU486. In addition, we observed a concomitant decrease in RXR (retinoid X receptor) mRNA levels, the obligatory partner of both CAR and PXR for high affinity binding to DNA. These findings represent one possible molecular mechanism underlying sepsis-induced repression of Cyp enzymes.

Animals↗
PubMed1970

Metabolic influences on tyrosine excretion in Bacillus subtilis.

The biosynthetic pathway for tyrosine synthesis is regulated both by repression of enzyme synthesis and by feedback inhibition of enzyme activity in Bacillus subtilis. Nevertheless, wild-type cells produce significantly more tyrosine than is required for protein synthesis, and part of this is excreted into the medium. Alteration of nutritional and other environmental conditions of cultivation strongly influenced the amount of tyrosine excretion. The excretion of tyrosine by wild-type cells was compared with that of a regulatory mutant having a feedback-insensitive prephenate dehydrogenase. Tyrosine excretion varied directly with the in vitro activity of prephenate dehydrogenase and inversely with temperature in the two strains. The regulatory mutant excreted five times as much tyrosine as the wild type at all growth temperatures examined. The carbon source used for growth significantly influenced the level of tyrosine excretion. The specific activity of prephenate dehydrogenase was also affected by the carbon source. Incorporation studies with isotopic tyrosine and fluorometric determinations of tyrosine concentrations extractable in hot water were used to measure operationally the tyrosine pools in the mutant and wild-type strains. The effects of various environmental conditions on the synthesis and excretion of tyrosine led to the conclusion that metabolic controls governing end product contrations exist which are completely independent of regulation by feedback inhibition and repression.

Bacillus subtilis↗
PubMed1965

FURTHER STUDIES ON THE REGULATION OF AMINO SUGAR METABOLISM IN BACILLUS SUBTILIS.

1. Glucosamine 6-phosphate deaminase [2-amino-2-deoxy-d-glucose 6-phosphate ketol-isomerase (deaminating), EC 5.3.1.10] of Bacillus subtilis has been partially purified. Its K(m) is 3.0mm. 2. Extracts of B. subtilis contain N-acetylglucosamine 6-phosphate deacetylase (K(m) 1.4mm), glucosamine 1-phosphate acetylase and amino sugar kinases (EC 2.7.1.8 and 2.7.1.9). 3. Glucosamine 6-phosphate synthetase (l-glutamine-d-fructose 6-phosphate aminotransferase, EC 2.6.1.16) is repressed by growth of B. subtilis in the presence of glucosamine, N-acetylglucosamine, N-propionylglucosamine or N-formylglucosamine. Glucosamine 6-phosphate deaminase and N-acetylglucosamine 6-phosphate deacetylase are induced by N-acetylglucosamine. Amino sugar kinases are induced by glucose, glucosamine and N-acetylglucosamine. The synthesis of glucosamine 1-phosphate acetylase is unaffected by amino sugars. 4. Glucose in the growth medium prevents the induction of glucosamine 6-phosphate deaminase and of N-acetylglucosamine 6-phosphate deacetylase caused by N-acetylglucosamine; glucose also alleviates the repression of glucosamine 6-phosphate synthetase caused by amino sugars. 5. Glucosamine 6-phosphate deaminase increases in bacteria incubated beyond the exponential phase of growth. This increase is prevented by glucose.

Acetylglucosamine↗
PubMed1978

[Interrelationships between carnitine metabolism and fatty acid assimilation in Pseudomonas putida (author's transl)].

The carnitine metabolism and some relations to the fatty acid metabolism were studied in Pseudomonas putida by means of control of growth, analysis of metabolites, and determination of enzyme activites. The strain grew on gamma-butyrobetaine, D,L- and L-carnitine, glycinebetaine, choline, D,L-norcarnitine, D,L-gamma-amino-beta-hydroxybutyrate, and D,L-beta-hydroxybuty-rate. Although the strain used straight-chain fatty acids of 2-16 C-atoms, it was only able to grow on O-acyl-L-carnitines of 10 or more C-atoms in the acyl-group. Addition of carnitine stimulated the growth on long-chain fatty acis. The formation of trimethylamine increased, if L-carnitine or gamma-butyrobetaine were the only carbon sources, and decreased, if these trimethylammonium compounds were carbon as well as nitrgen sources. L-Carnitine induced the carnitine dehydrogenase as well as the beta-hydroxybutyrate dehydrogenase, gamma-Butyrobetaine as carbon and nitrogen source induced the carnitine dehydrogenase, too. In the crude extract the specific activiteis of beta-hydroxybutyrate dehydrogenase were 0.7 or 1.6 mumoles.min-1.mg-1 after growth on L-carnitine and D,L-beta-hydroxybutyrate, respectively. The synthesis of both enzymes was repressed by glycinebetaine, glucose and long-chain fatty acis. Dependent on the nitrogen source L-carnitine was catabolized via two different pathways.

Animals↗
PubMed1980

The use of phenylmethylsulfonyl fluoride in the study of catabolite inactivation and repression in intact cells of Saccharomyces cervisiae.

Catabolite inactivation of fructose-1,6-bisphosphatase, isocitrate lyase, phosphoenolpruvate carboxykinase and malate dehydrogenase in intact cells could be prevented by phenylmethylsulfonyl fluoride added 40 min prior to the addition of glucose. Protein synthesis, fermentative and respiratory activity and catabolite repression were not affected. Elimination of catabolite inactivation by the addition of PMSF revealed that catabolite repression started at different times for different enzyme.

Enzyme Repression↗
PubMed1976

CO2-fixing enzymes in Pseudomonas fluorescens.

Pseudomonas fluorescens grown on glucose or glutamate at 1 or 20 degrees C, or on acetate at 20 degrees C, as sole carbon sources, contained both pyruvate carboxylase and phosphoenolpyruvate carboxylase. Pyruvate carboxylase was insensitive to acetyl-coenzyme A and L-aspartate, and its level in cell-free extracts was markedly dependent on the carbon source for growth, the highest specific activity being attained in glucose-grown cells. Phosphoenolpyruvate carboxylase, on the other hand, although less dependent on the nature of the carbon source,showed its highest level in acetate-grown cells; the enzyme activity required acetyl-coenzyme A and was strongly inhibited by L-aspartate. The micro-organism had, in addition, a phosphoenolpyruvate carboxykinase, which showed its highest specific activity in cells grown on acetate, and a NADP-linked malate enzyme, apparently repressed by acetate and showing its highest specific activity in glutamate-grown cells.

Acetates↗
PubMed1996

Physiological factors affecting production of extracellular lipase (LipA) in Acinetobacter calcoaceticus BD413: fatty acid repression of lipA expression and degradation of LipA.

The extracellular lipase (LipA) produced by Acinetobacter calcoaceticus BD413 is required for growth of the organism on triolein, since mutant strains that lack an active lipase fail to grow with triolein as the sole carbon source. Surprisingly, extracellular lipase activity and expression of the structural lipase gene (lipA), the latter measured through lacZ as a transcriptional reporter, are extremely low in triolein cultures of LipA+ strains. The explanation for this interesting paradox lies in the effect of fatty acids on the expression of lipA. We found that long-chain fatty acids, especially, strongly repress the expression of lipA, thereby negatively influencing the production of lipase. We propose the involvement of a fatty acyl-responsive DNA-binding protein in regulation of expression of the A. calcoaceticus lipBA operon. The potential biological significance of the observed physiological competition between expression and repression of lipA in the triolein medium is discussed. Activity of the extracellular lipase is also negatively affected by proteolytic degradation, as shown in in vitro stability experiments and by Western blotting (immunoblotting) of concentrated supernatants of stationary-phase cultures. In fact, the relatively high levels of extracellular lipase produced in the early stationary phase in media which contain hexadecane are due only to enhanced stability of the extracellular enzyme under those conditions. The rapid extracellular degradation of LipA of A. calcoaceticus BD413 by an endogenous protease is remarkable and suggests that proteolytic degradation of the enzyme is another important factor in regulating the level of active extracellular lipase.

Acinetobacter calcoaceticus↗