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PubMed1978

Regulation of enzyme synthesis in the arginine biosynthetic pathway of Pseudomonas aeruginosa.

In Pseudomonas aeruginosa the synthesis of only two out of eight arginine biosynthetic enzymes tested was regulated. Comparisons were made between the specific activities of these enzymes in bacteria grown on arginine or on its precursor, glutamate. N2-Acetylornithine 5-aminotransferase (ACOAT), an enzyme involved in both the biosynthesis and catabolism of arginine, was induced about 14-fold during growth of the organism on arginine as the only carbon and nitrogen source, and the anabolic ornithine carbamoyltransferase (aOTC), a strictly biosynthetic enzyme, was repressed 18-fold. Addition of various carbon sources to the arginine medium led to repression of ACOAT and to derepression of aOTC. Fructose, which supported only slow growth of P. aeruginosa, had a weak regulatory effect on the synthesis of the two arginine enzymes while citrate, a good carbon source for this organism, had a strong effect. The repression of ACOAT by citrate was not relieved by adding cyclic AMP to the medium. Under a variety of growth conditions leading to different enzyme activities, a linear relationship between the reciprocal of the specific activity of ACOAT and the specific activity of aOTC was observed. This inverse regulation of the formation of the two enzymes suggested that a single regulatory system governs their synthesis. Such a view was supported by the isolation of citrate-resistant regulatory mutants which constitutively formed ACOAT at the induced level and aOTC at the repressed level.

Arginine↗
PubMed2001

Regulation of cellulases and xylanases from a derepressed mutant of Cellulomonas flavigena growing on sugar-cane bagasse in continuous culture.

When the wild type Cellulomonas flavigena was grown on glycerol, xylose or cellobiose, it produced basal levels of carboxymethyl-cellulase (CMCase), filter-paperase (FPase) and xylanase activities. By comparison, a catabolic derepressed mutant strain of the same organism produced markedly higher levels of these enzymes when grown on the same carbon sources. Sugar-cane bagasse induced both the wild type and the mutant strain to produce three- to eight-time higher levels of FPase and xylanase than was observed with xylose or cellobiose. Continuous culture was used to determine the minimal cellobiose or glucose concentrations that repress the enzyme synthesis in both strains. 2.5 g l(-1) glucose repressed FPase and xylanases from wild type, while 1.6 times more glucose was needed to repress the same activities in the PN-120 strain. In the same way, twofold more cellobiose was needed to reduce by 75% the CMCase and xylanase activities in the mutant compared to the wild type. The FPase in the presence of 4 g l(-1) cellobiose did not change in the same strain. Therefore, its derepressed and feedback resistant characters of PN-120 mutant are evident. On the other hand, isoelectrofocused crude extracts of mutant and wild strains induced by sugar-cane bagasse, did not show differences in protein patterns, however, the Schiffs staining was more intense in the PN-120 than in the wild strain. These results point out that the mutational treatment did not apparently change the extracellular proteins from mutant PN-120 and this could affect their regulation sites, since derepressed and feed-back resistant enzymes may be produced.

Actinomycetales↗
PubMed1985

Alcohol dehydrogenase II and fructose-1,6-bisphosphatase appear to be co-regulated in wild-type yeast.

An activity gel assay for fructose-1,6-bisphosphatase (FBP), the enzyme catalyzing the final step in gluconeogenesis in yeast, has been developed which can be used in conjunction with spectrophotometric assays to show that it is tightly co-regulated with the inducible alcohol dehydrogenase, ADHII. Both enzymes are repressed coordinately in aerobically grown yeast by the addition of high levels of glucose or ethanol, and induced on minimal medium by the addition of yeast extract. A mutant deficient in FBP segregates independently of the ADHII structural gene locus. This phenomenon is of interest because of the discovery of Ciriacy [(1979) Mol. Gen. Genet. 176, 427-431] of mutants (ccr, or carbon catabolite repression) which repress both FBP and ADHII simultaneously, along with several other enzymes.

Alcohol Dehydrogenase↗
PubMed1981

Constitutive behavior of methionyl-tRNA synthetase compared to repressible behavior of methionine adenosyltransferase in mammalian cells.

Methionine adenosyltransferase, one of the two major enzymes utilizing methionine, is regulated by the levels of methionine in the growth medium (Jacobsen, S.J., Hoffman, R.M. and Erbe, R.W. (1980) J. Natl. Cancer Inst. 65, 1237--1244, and Caboche, M. and Mulsant, P. (1978) Somatic Cell Genet. 4, 407--421). We report here that methionyl-tRNA synthetase, unlike methionine adenosyltransferase, behaves in a constitutive manner with respect to the concentration of methionine in the culture medium. This behavior is seen in Chinese hamster ovary cells and in normal diploid and SV40-transformed human fibroblasts. Although the kinetics of regulation of methionine adenosyltransferase and methionyl-tRNA synthetase by exogenous methionine are clearly different, the levels of the two enzymes in the human cell lines are similar.

Amino Acyl-tRNA Synthetases↗
PubMed1990

Regulation of assimilatory nitrate reductase formation in Klebsiella aerogenes W70.

Klebsiella aerogenes W70 could grow aerobically with nitrate or nitrite as the sole nitrogen source. The assimilatory nitrate reductase and nitrite reductase responsible for this ability required the presence of either nitrate or nitrite as an inducer, and both enzymes were repressed by ammonia. The repression by ammonia, which required the NTR (nitrogen regulatory) system (A. Macaluso, E. A. Best, and R. A. Bender, J. Bacteriol. 172:7249-7255, 1990), did not act solely at the level of inducer exclusion, since strains in which the expression of assimilatory nitrate reductase and nitrite reductase was was independent of the inducer were also susceptible to repression by ammonia. Insertion mutations in two distinct genes, neither of which affected the NTR system, resulted in the loss of both assimilatory nitrate reductase and nitrite reductase. One of these mutants reverted to the wild type, but the other yielded pseudorevertants at high frequency that were independent of inducer but still responded to ammonia repression.

Ammonia↗
PubMed1977

Control of beta-glucosidase synthesis in Mucor racemosus.

The beta-glucosidase of Mucor racemosus was shown to be synthesized when the organism was grown in the presence of such diverse carbon sources as glycerol, lactate, xylose, ribose, alpha-methylglucoside, alpha-phenylglucoside, maltose, and cellobiose. Enzyme synthesis was strongly repressed in the presence of hexoses. In addition, exogenous cyclic adenosine 3',5'-monophosphate (cAMP) resulted in enzyme repression. When cAMP was added exogenously after enzyme activity had accumulated, a reversible enzyme inactivation occurred. Growth on disaccharides (maltose or cellobiose) was severely retarded in the presence of cAMP, whereas that on glucose remained unaffected. The results indicate a probable role for cAMP in control of glucosidase synthesis in Mucor.

Carbon↗
PubMed1969

Relationships between the regulation of the lactose and galactose operons of Escherichia coli.

A group of structurally related compounds, including galactose, fucose, and a number of galactosides, are regulatory effectors for both the lac and gal operons of Escherichia coli. Although a common set of effectors exists, each operon appears to be regulated independently of the other. Experiments with various regulatory mutants have shown, first, that the presence of the proteins of one operon is without effect on the regulation of the other and, second, that the influence an effector has on one operon is independent of the presence or the functional state of the regulatory genes of the other operon. It is unlikely, therefore, that the two operons share a common regulatory macromolecule. Both gal R(-) and gal o(c) regulatory mutants are equally resistant to repression by glucose and galactosides. It has been possible to show, in the gal operon, that induction and repression are competitive processes. For this operon, the differential rate of enzyme synthesis is set by the relative intracellular concentrations of inducer (fucose) and repressor (isopropylthiogalactoside).

Enzyme Induction↗
PubMed1983

Regulation of creatine phosphokinase expression during differentiation of BC3H1 cells.

The intracellular mechanisms involved in the regulation of creatine phosphokinase expression in the BC3H1 muscle-like cell line have been examined under conditions of enzyme induction and repression. In the presence of low serum concentrations, BC3H1 cells cease to grow and synthesize high levels of creatine phosphokinase. When differentiated BC3H1 cultures are exposed to media containing high serum concentrations, cell division is reinitiated and further induction of creatine phosphokinase is inhibited. Accumulation of creatine phosphokinase-mRNA appears to be intimately coupled to the state of growth of BC3H1 cells. Log phase cells do not contain detectable levels of translatable creatine phosphokinase-mRNA; however, following cessation of growth, creatine phosphokinase-mRNA accumulates in approximate proportion to the increase in creatine phosphokinase activity. Reinitiation of cell division in quiescent differentiated cultures results in the arrest of further accumulation of creatine phosphokinase-mRNA but does not inhibit the translation of pre-existing creatine phosphokinase-mRNA. Under conditions of enzyme repression, however, the newly synthesized creatine phosphokinase appears to be enzymatically inactive. These results indicate that the expression of the muscle phenotype in BC3H1 cells is regulated by components present in serum and that myogenic differentiation is at least partially reversible following re-entry of quiescent cells into the cell cycle.

Animals↗
PubMed1979

Action of oestrogens and antioestrogens on oestrogen-inducible cytoplasmic and androgen-inducible microsomal activity of 3 alpha-hydroxysteroid dehydrogenase in male rat kidney.

The influence of steroidal and non-steroidal antioestrogenic compounds on the effect of systemically administered oestradiol (OE2) and diethylstilboestrol (DES) was investigated in adult male rats with intact gonads. In this animal model, oestrogens induced the NADP-dependent cytoplasmic activity and prevented the inductive action of androgens on NADP-dependent microsomal activity of renal 3 alpha-hydroxysteroid dehydrogenase (3 alpha-HSDH). Simultaneous administration of tamoxifen (0.5 mg/day) with OE2 (5 microgram/day) or DES (10 microgram/day) for 10 days completely blocked the inductive effect of OE2 on cytoplasmic 3 alpha-HSDH, whereas, in the case of the microsomal enzyme, the repressive effects of OE2 and DES were antagonized only to 28 and 16% respectively. Simultaneous administration of 5 alpha-dihydrotestosterone (DHT; 0.5 mg/day) for 10 days antagonized the inductive effect of OE2 on the cytoplasmic enzyme activity to 86% and completely by-passed the repressive effects of OE2 and DES on the microsomal enzyme activity. It is concluded that oestrogenic induction of renal cytoplasmic 3 alpha-HSDH involves an oestrogen receptor mechanism which, in this animal model, can be antagonized by tamoxifen. In contrast, oestrogenic repression of renal microsomal 3 alpha-HSDH is obviously the consequence of the strong antigonadotrophic activity of oestrogens leading to subsequent repression of testicular androgen secretion by mechanisms which can be only weakly antagonized by tamoxifen. Exogenous DHT, even in the presence of OE2 or DES, completely compensates for this centrally mediated deficit of peripheral androgen.

3-Hydroxysteroid Dehydrogenases↗
PubMed2002

DNA methyltransferase and demethylase in human prostate cancer.

Recent studies have shown that cytosine-5 methylation at CpG islands in the regulatory sequence of a gene is one of the key mechanisms of inactivation. The enzymes responsible for CpG methylation are DNA methyltransferase (DNMT) 1, DNMT3a, and DNMT3b, and the enzyme responsible for demethylation is DNA demethylase (MBD2). Studies on methylation-demethylation enzymes are lacking in human prostate cancer. We hypothesize that MBD2 enzyme activity is repressed and that DNMT1 enzyme activity is elevated in human prostate cancer. To test this hypothesis, we analyzed enzyme activities, mRNA, and protein levels of MBD2 and DNMT1, DNMT3a, and DNMT3b in human prostate cancer cell lines and tissues. The enzyme activities of DNMTs and MBD2 were analyzed by biochemical assay. The mRNA expression was analyzed by reverse transcriptase-polymerase chain reaction and by Northern blotting. The protein expression was measured by immunohistochemistry with specific antibodies. The results of these experiments demonstrated that (1) the activity of DNMTs was twofold to threefold higher in cancer cell lines and cancer tissues, as compared with a benign prostate epithelium cell line (BPH-1) and benign prostatic hyperplasia (BPH) tissues; (2) MBD2 activity was lacking in prostate cancer cell lines but present in BPH-1 cells; (3) immunohistochemical analyses exhibited higher expression of DNMT1 in all prostate cancer cell lines and cancer tissues, as compared with BPH-1 cell lines and BPH tissues; (4) MBD2 protein expression was significantly higher in BPH-1 cells and lacking in prostate cancer cell lines and, in BPH tissues, MBD2 protein expression was poorly observed, as compared with no expression in prostate cancer tissues; and (5) mRNA expression for DNMT1 was upregulated in prostate cancer, as compared with BPH-1, and mRNA expression for MBD2 was found to be significantly expressed in all cases. The results of these studies clearly demonstrate that DNMT1 activity is upregulated, whereas MBD2 is repressed at the level of translation in human prostate cancer. These results may demonstrate molecular mechanisms of CpG hypermethylation of various genes in prostate cancer.

Cell Line↗
PubMed1994

Inducibility of the TOL catabolic pathway in Pseudomonas putida (pWW0) growing on succinate in continuous culture: evidence of carbon catabolite repression control.

The TOL catabolic genes in Pseudomonas putida (pWW0) are clustered in the upper operon, encoding enzymes for the conversion of toluene and xylenes to benzoate and toluates, and the meta-cleavage operon, encoding enzymes for the conversion of the benzoate and toluates to tricarboxylic acid cycle intermediates. In this study, it was shown that cells growing in a chemostat under succinate growth-limiting conditions express both the upper and meta-cleavage pathways in response to o-xylene, a nonmetabolizable effector of the XylR regulatory protein. The dilution rate maintained in the succinate-limited chemostat cultures influenced the synthesis levels of TOL pathway enzymes, their steady-state levels, and their turnover rates. Cells growing in the presence of nonlimiting concentrations of succinate in continuous culture did not express pathway enzymes in response to the addition of o-xylene, which was due to a blockage at the transcriptional level. Expression of the meta-cleavage pathway in response to 2,3-dimethylbenzoate, a nonmetabolizable effector of the XylS regulatory protein, was 93% lower in cultures exposed to succinate at nonlimiting concentrations than in the succinate-limited chemostats. The mRNA level of xylS during nonlimited growth on succinate was very low compared with that in succinate-limited cultures, suggesting that suppression of expression of the meta-cleavage pathway is regulated mainly by the level of the XylS regulator.

Base Sequence↗