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Results for “Enzyme Repression”

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At least 433 records · Page 24Linked to original sources
PubMed1977

The tricarboxylic and acid pathway in Desulfovibrio.

Strains of two species of Desulfovibrio were examined for enzymes of the tricarboxylic acid cycle and related pathways. Pyruvate carboxylase (EC6.4.1.1) is present, and alpha-ketoglutarate is formed via the tricarboxylic acids. Glutamate, but not succinyl-CoA, arises from alpha-ketoglutarate. A pathway exists from pyruvate by malic enzyme (EC 1.1.1.39) activity to malate, then fumarate and succinate, again with no evidence of succinyl-CoA formation. The enzymes concerned with metabolism of these dicarboxylic acids show greater activity in the strains that can grow by fumarate dismutation. Glutamate (or glutamine), alpha-ketoglutarate, and yeast extract repress the enzymes that metabolize the tricarboxylic acids. There appears to be no glyoxylate cycle in Desulfovibrio vulgaris or D. desulfuricans.

Anaerobiosis↗
PubMed1975

Two forms of guanylate cyclase in mammalian tissues and possible mechanisms for their regulation.

All mammalian tissues examined to date have two forms of guanylate cyclase with apparently different properties. From the studies in several laboratories, we suggest the following mechanisms for the possible regulation of guanylate cyclase activity: (1) factors that could alter the apparent cooperative nature of the enzyme, (2) interactions of metal ions with the substrate or enzyme, (3) factors that could overcome inhibition by ATP, (4) mechanisms that could regulate the interconversion of latent and active forms of the enzyme, (5) possible translocation of particulate and soluble forms of the enzyme, and (6) induction or repression of the enzyme.

Allosteric Regulation↗
PubMed1972

Mutant of Escherichia coli with derepressed levels of the biotin biosynthetic enzymes.

A cross-feeding technique was used to isolate a mutant of Escherichia coli K-12 that excretes 1,000 times more biotin into the growth medium than the parent strain. The mutant has high levels of the biotin biosynthetic enzymes even when grown in the presence of biotin. Desthiobiotin synthetase, the level of which was used as a measure of the biosynthetic activity of the biotin pathway, is not repressed by biotin at the concentration 250,000 times that sufficient to repress the enzyme in the wild type. The mutant gene is cotransducible with argC located at 77 min on the E. coli chromosome.

Acetates↗
PubMed1977

Regulation of the arginine dihydrolase pathway in Clostridium sporogenes.

Arginine deiminase activity was induced during the vegetative growth of Clostridium sporogenes. The enzyme was sensitive to catabolite repression. The other enzymes of the arginine dihydrolase pathway, namely, ornithine carbamoyl-transferase and carbamate kinase, did not show such variation.

Arginine↗
PubMed1974

Nitrogen repression of the allantoin degradative enzymes in Saccharomyces cerevisiae.

Saccharomyces cerevisiae can utilize allantoin as a sole nitrogen source by degrading it to ammonia, "CO(2)," and glyoxylate. We have previously shown that synthesis of the allantoin degradative enzymes is contingent upon the presence of allophanate, the last intermediate in the pathway. The reported repression of arginase by ammonia prompted us to ascertain whether or not the allantoin degradative system would respond in a similar manner. We observed that the differential rates of allantoinase and allophanate hydrolase synthesis were not decreased appreciably when comparing cultures grown on urea to those grown on urea plus ammonia. These experiments were also performed using the strain and conditions previously reported by Dubois, Grenson, and Wiame. We found allophanate hydrolase production to be twofold repressed by ammonia when that strain was grown on glucose-urea plus ammonia medium. If, however, serine or a number of other readily metabolized amino acids were provided in place of ammonia, production of the allantoin degradative enzymes was quickly (within 20 min) and severely repressed in both strains. We conclude that repression previously attributed to ammonia may result from its metabolism to amino acids and other metabolites.

Alanine↗
PubMed1972

Oxidation of nicotinic acid by a Bacillus species: regulation of nicotinic acid and 6-hydroxynicotinic acid hydroxylases.

The first two enzymes employed by a Bacillus species for the dissimilation of nicotinic acid are coordinately induced. The inducer of the enzymes appears to be 6-hydroxynicotinic acid, the product of the first enzyme in the pathways. Synthesis of the enzymes is repressed by glucose when ammonium is present in the medium, but not when nicotinic acid is the sole nitrogen source. The possible significance of the coordinate induction and unusual repression is discussed.

Bacillus↗