Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Enzyme Repression”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 613 records · Page 34Linked to original sources
PubMed1981

Alpha-isopropylmalate synthase as a marker for the leucine biosynthetic pathway in several clostridia and in Bacteroides fragilis.

Alpha-Isopropylmalate synthase (EC 4.1.3.12) is present in extracts of Bacteroides fragilis, Clostridium thermoaceticum, Clostridium formicoaceticum, Clostridium pasteurianum, and Clostridium kluyveri with specific activities (micromol alpha-isopropylmalate formed per min and g protein) of 8.6, 8.9, 2.4, 1.9, and 0.3, respectively. The product alpha-isopropylmalate was identified by gas chromatography combined with mass spectroscopy. The presence of 5mM leucine in the growth medium represses the synthesis of alpha-isopropylmalate synthase in C. thermoaceticum by 40 and 70%. The enzyme from c. pasteurianum was partially purified to a specific activity of 1413. All studied enzyme properties are similar to those of the enzymes from aerobic bacteria. It is suggested that in these anaerobic bacteria the alpha-isopropylmalate pathway is present in addition to the pathway via the ferrodoxin-dependent, reductive carboxylation of branched chain fatty acids.

2-Isopropylmalate Synthase↗
PubMed1975

Methionine-and S-adenosyl methionine-mediated repression in a methionyl-transfer ribonucleic-acid synthetase mutant of Saccharomyces cerevisiae.

A Saccharomyces cerevisiae mutant strain unable to grow at 38 C and bearing a modified methionyl-transfer ribonucleic acid (tRNA) synthetase has been studied. It has been shown that, in this mutant, the percentage of tRNAmet charged in vivo paralleled the degree of repressibility of methionine biosynthetic enzymes by exogenous methionine. On the contrary, the repression mediated by exogenous S-adenosylmethionine does not correlate with complete acylation of tRNAmet. Althought McLaughlin and Hartwell reported previously that the thermosensitivity and the defect in the methionyl-tRNA synthetase were due to the same genetic lesion (1969), no diffenence could be found in the methionyl-tRNA synthetase activity or in the pattern of repressibility of methionine biosynthetic pathway after growth at the premissive and at a semipermissive temperature. It appears that the mutant also exhibits some other modified characters that render unlikely the existence of only one genetic lesion in this strain. A genetic study of this mutant was undertaken which led to the conclusion that the thermosensitivity and the other defects are not related to the methionyl-tRNA synthetase modification. It was shown that the modified repressibility of methionine biosynthetic enzymes by methionine and the lack of acylation of tRNAmet in vivo follow the methionyl-tRNA synthetase modification. These results are in favor of the idea that methionyl-tRNAmet, more likely than methionine, is implicated in the regulation of the biosynthesis of methionine.

Amino Acyl-tRNA Synthetases↗
PubMed1981

Nutrient utilization in actinomycetes. Induction of alpha-glucosidases in Streptomyces venezuelae.

Streptomyces venezuelae contains intracellular alpha-glucosidases that are induced during growth on maltose, isomaltose, maltotriose, dextrin, starch, and other alpha-glucosides. Induction was prevented by rifampicin at 10 micron g.mL-1 and inhibited by chloramphenicol or streptomycin, indicating that de novo synthesis of messenger ribonucleic acid and protein was required. Glucose and other readily utilizable sugars did not repress induction of alpha-glucosidase activity whereas certain organic acids and amino acids effectively reduced enzyme synthesis. Extracts of mycelium grown in the presence of maltose as an inducer hydrolysed maltose and isomaltose rapidly. Sucrose and other alpha-glucosides were less suitable substrates whereas trehalose and starch were not hydrolysed. No activity was observed with Beta-glucosides, alpha-galactosides, or methyl alpha-mannoside.

Chloramphenicol↗
PubMed1994

Isolation and preliminary characterization of Pichia pinus mutants insensitive to glucose repression.

A new method for the isolation of glucose repression-insensitive mutants in the methylotrophic yeast Pichia pinus was developed. The method is based on screening of small suspension samples derived from 2-deoxyglucose-resistant colonies for alcohol oxidase activity. Alcohol oxidase activity was evaluated by determination of formaldehyde excreted by cells. Mutants with glucose non-repressible alcohol oxidase and catalase synthesis were obtained. All mutants grew poorly on D-xylose compared to the wild type, whereas growth on L-arabinose was similar to the wild type. Changes in the glucose transport system were suggested to be responsible for altered growth characteristics and defective glucose repression.

Alcohol Oxidoreductases↗
PubMed1985

Repression and inhibition of cephalosporin synthetases in Streptomyces clavuligerus by inorganic phosphate.

Cephalosporin production by growing cells of Streptomyces clavuligerus was reduced by 100 mM inorganic phosphate. Resting cell production was repressed by prior growth in high phosphate and inhibited by phosphate. The cell-free activity of desacetoxycephalosporin C synthetase (ring expansion activity) was repressed by prior growth in high phosphate and inhibited by phosphate. Isopenicillin N synthetase (cyclase) was inhibited but not repressed. Penicillin epimerase was neither inhibited nor repressed by phosphate.

Cephalosporins↗
PubMed1976

Catabolite modulator factor: a possible mediator of catabolite repression in bacteria.

Water soluble extracts of Escherichia coli cells have been found to exert an extremely strong repressive effect upon the expression of catabolite sensitive operons. The compound responsible for this activity has been partially purified and proves to be of low molecular weight and heat stable. The effect of this compound, hereafter designated as catabolite modulator factor, is only partially antagonized by adenosine 3':5'-cyclic monophosphate. The possible role of catabolite modulator factor in the physiological regulation of catabolite repression is discussed.

Cyclic AMP↗
PubMed1978

Repression of biotin biosynthesis in Escherichia coli during growth on biotin vitamers.

A strain of Escherichia coli in which the lacZ gene was fused to the bioA promoter was constructed. Colonies of this strain formed Lac(+) colonies on low-biotin agar (1.6 to 4.1 nM) and Lac(-) colonies on high-biotin agar (41 nM). This lac-bio fusion strain was used to study the question of whether cells growing on the biotin vitamers d-biotin-d-sulfoxide (BDS) and dethiobiotin (DTB) generate enough biotin to give maximal repression of beta-galactosidase synthesis. Repression by high concentrations (400 nM) of BDS was almost maximal (about 96%), whereas DTB repression reached a saturation level of about 80% with increasing DTB concentrations. The levels of repression obtained with both vitamers were sufficient to cause the colonies to appear Lac(-). When the lac-bio fusion was transduced into lines carrying mutations (bis) that prevent reduction of BDS to biotin, the transductants were not repressed by added BDS. Repression by BDS is unlikely to result from accumulation of extracellular biotin-related substances because (i) washed bis(+) cells were not detectably derepressed when transferred into medium containing BDS and (ii) washed bis cells were not detectably repressed when transferred into medium in which bis(+) cells had grown. Lactose agar plates containing high concentrations of DTB or BDS comprise an efficient selective medium for bioB or bis mutants and were used to isolate spontaneous mutations of these genes. This method should be adaptable to the selection of mutations in any biosynthetic pathway subject to end-product repression.

Biotin↗
PubMed1979

Nitrogen metabolite repression of nitrate reductase in Neurospora crassa.

The effect of different nitrogen compounds on the induction of reduced nicotinamide adenine dinucleotide phosphate-nitrate reductase was examined in Neurospora crassa. Whereas in the wild-type strain several amino acids and ammonia inhibit the formation of nitrate reductase, only glutamine, cysteine, and histidine are shown to inhibit the synthesis of nitrate reductase in a glutamine-requiring auxotroph. None of the amino acids inhibited nitrate reductase activity in vitro. The effects of cysteine and histidine are nonspecific, these amino acids being inhibitory of the growth of the organism. The effect of glutamine on the induction of nitrate reductase is not due to an inhibition of the uptake of the inducer nitrate. By the use of histidine-, pyrimidine-, and arginine-requiring auxotrophs, it was shown that glutamine appears to act per se and does not seem to be converted to another product in order to be effective in repression. The repression of nitrate reductase by ammonia appears, from the results described herein, to be indirect; ammonia has to be converted first to glutamine in order to be effective in repression.

Amino Acids↗
PubMed1983

Effects of aerobic and anaerobic shock on catabolite repression in cyclic AMP suppressor mutants of Escherichia coli.

Cultures of Escherichia coli K-12 grown on glucose or gluconate under aerobic conditions exhibited catabolite repression of beta-galactosidase synthesis. Depression occurred when these cultures were subjected to anaerobic shock. These states of repression and depression were found to be associated with low and high differential rates of cyclic AMP synthesis, respectively. This observation is consistent with the view that cyclic AMP plays a central role in the catabolite repression phenomenon. We report here, however, that identical stages of repression and derepression occur in mutant strains possessing cya crp(Csm) genotypes and therefore unable to synthesize cyclic AMP. These results suggest that cyclic AMP is not the sole regulator involved in catabolite repression.

Aerobiosis↗
PubMed1984

Gratuitous repression of avtA in Escherichia coli and Salmonella typhimurium.

avtA , which encodes transaminase C (alanine-valine transaminase), is repressed by excess-L-alanine or L-leucine, and also by limitation for any of a number of amino acids in Escherichia coli and Salmonella typhimurium. Amino acid limitation causes repression by promoting the accumulation of L-alanine or L-leucine or both. avtA is also repressed by L-alpha-aminobutyric acid and other nonprotein amino acids which are structurally similar to L-alanine. We hypothesize that L-alanine and L-alpha-aminobutyric acid, whose syntheses are catalyzed by transaminase C, are the true corepressors of avtA . Repression by structural analogs of the true corepressors is termed gratuitous repression.

Alanine↗