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PubMed1997

Characterization of an extracellular keratinase of Trichophyton simii and its role in keratin degradation.

The ability of Trichophyton simii HN 50, isolated from the Ghana Bird Sanctuary, Bharatpur, India, to produce extracellular keratinase was studied. Enzyme was produced on a keratin salt broth medium at pH7 and a temperature of 28 +/- 1 degree C. Enzyme secretion was best at 15 days of incubation. Asparagine and keratin were repressive to enzyme yield in comparison to gelatin. No relationship was observed between enzyme release and biomass sugars suppressed keratinase production in descending order as follows: glucose > mannose > maltose > arabinose > fructose. The enzyme showed ability to degrade all of the 3 keratin substrates. Buffalo skin was best degraded in the absence of glucose while chicken feathers were the least degraded in its presence.

Animals↗
PubMed1970

Comparative metabolism of vegetative and sporulating cultures of Clostridium thermosaccharolyticum.

Cultures of Clostridium thermosaccharolyticum, under conditions of restricted growth achieved by slow feeding of glucose, showed a high degree of sporulation. Analysis of the end products showed an accumulation of ethyl alcohol in addition to butyrate and acetate, whereas, in the nonsporulating cultures, acetate and butyrate were the principal products. Incorporation of uniformly labeled (14)C-glucose by sporulating cells was three to four times higher than by nonsporulating cells. The efficiency of acetate assimilation into the lipid fraction of sporulating cells was at least two times higher than that of glucose. When starch was used as the carbon source, the growth rate was reduced; sporulation occurred, and the end products and carbon distribution were similar. Alcohol dehydrogenase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase were preferentially formed by sporulating cells. In vegetative cells, the formation of these enzymes was repressed if the glucose concentration in the medium was increased. The change in enzyme activity appeared to be related to a morphological change in the cells and indicated an altered metabolic pattern for sporulating cells.

Acetates↗
PubMed1977

Nitrogen regulation of arginase in Neurospora crassa.

The final products of the arginine catabolism that can be utilized as a nitrogen source in Neurospora crassa are ammonium, glutamic acid, and glutamine. The effect of these compounds on arginase induction by arginine was studied. In wild-type strain 74-A, induction by arginine was almost completely repressed by glutamic acid plus ammonium, whereas ammonium or glutamic acid alone had only moderate effects. Arginine products of catabolism also repressed arginase induction. A mutant, ure-1, which lacks urease activity, hyperinduced its arginase with arginine as a nitrogen source. The addition of either ammonium or glutamine produced effects similar to those in the wild-type strain. The effect of ammonium on arginase induction is mediated through its conversion into glutamine. This was demonstrated in mutant am-1, which lacks L-glutamate dehydrogenase activity. In this mutant, the effect of glutamic acid was reduced, and, with ammonium, it was completely lost. The addition of glutamine or glutamic acid plus ammonium to this strain decreased by threefold the induction of arginase by arginine. Proline, a final product of arginine catabolism, competitively inhibited arginase activity. This effect and the repression of arginase by glutamine are examples of negative modulation of the first enzyme in a catabolic pathway by its final products.

Ammonia↗
PubMed1986

Short-term and long-term modulation of the enzymatic control of mutagenic and carcinogenic metabolites.

Many mutagenic and carcinogenic metabolites are controlled by several enzymes including activating, inactivating and precursor-sequestering enzymes. These enzymes themselves are, in turn, also subject to control which, usually, is also multiple, including enzyme induction, repression, activation and inhibition. For several classes of chemicals strong influences of such enzyme modulations on the mutagenicity have been elucidated. The effects of modulation of individual enzymes contributing to the control of a given mutagenic metabolite can be mutually antagonistic or potentiating and can markedly differ in their time frame, ranging from very short-term to extremely long-term modulation. Therefore, the complex interaction between all these modulations must be considered when evaluating the enzymatic control of mutagenic metabolites.

Animals↗
PubMed1980

The role fo glutamine synthetase and glutamine metabolism in nitrogen metabolite repression, a regulatory phenomenon in the lower eukaryote Neurospora crassa.

Growth of Neurospora crassa on media containing NH4+ leads to the repression of a variety of permeases and alternative pathways which would generate NH4+, so called "ammonium repression." The mutant am2 which lacks NADP-GDH is not subject to ammonium repression of nitrate reductase or urea permease, but like the wild type has repressed levels of these systems when grown in the presence of proline, glutamate or glutamine. The glutamine synthetase (GS) mutant gln-1a has derepressed levels of the aforementioned systems unless grown with glutamine. The oligomeric state of GS depends upon the nitrogen sufficiency of the cell, a tetrameric form predominates under conditions of nitrogen limitation and an octameric form under conditions of nitrogen sufficiency. We have found that the tetrameric form GS predominates in the mutants am2 and gln-1a when they are ammonium derepressed. Th mechanism of NH4+ repression in N. crassa is thought to entail a cessation of positive gene action by the product of the nit-2 regulatory gene. We propose that under conditions of NH4+ sufficiency, and hence glutamine sufficiency, the octameric form of GS represses nit-2 gene expression and thereby achieves ammonium repression.

Enzyme Repression↗
PubMed2002

Carbon catabolite repression in bacteria: choice of the carbon source and autoregulatory limitation of sugar utilization.

Carbon catabolite repression (CCR) in bacteria is generally regarded as a regulatory mechanism to ensure sequential utilization of carbohydrates. Selection of the carbon sources is mainly made at the level of carbohydrate-specific induction. Since virtually all carbohydrate catabolic genes or operons are regulated by specific control proteins and require inducers for high level expression, direct control of the activity of regulators or control of inducer formation is an efficient measure to keep them silent. By these mechanisms, bacteria are able to establish a hierarchy of sugar utilization. In addition to the control of induction processes by CCR, bacteria have developed global transcriptional regulation circuits, in which pleiotropic regulators are activated. These global control proteins, the catabolite gene activator protein (CAP), also known as cAMP receptor protein, in Escherichia coli or the catabolite control protein (CcpA) in Gram-positive bacteria with low GC content, act upon a large number of catabolic genes/operons. Since practically any carbon source is able to trigger global transcriptional control, expression of sugar utilization genes is restricted even in the sole presence of their cognate substrates. Consequently, CAP- or CcpA-dependent catabolite repression serves as an autoregulatory device to keep sugar utilization at a certain level rather than to establish preferential utilization of certain carbon sources. Together with other autoregulatory mechanisms that are not acting at the gene expression level, CCR helps bacteria to adjust sugar utilization to their metabolic capacities. Therefore, catabolic/metabolic balance would perhaps better describe the physiological role of this regulatory network than the term catabolite repression.

Bacteria↗
PubMed1966

Altered end-product patterns and catabolite repression in Escherichia coli.

Dobrogosz, Walter J. (North Carolina State University, Raleigh). Altered end-product patterns and catabolite repression in Escherichia coli. J. Bacteriol. 91:2263-2269. 1966.-End products formed during growth of Escherichia coli ML30 on glucose were examined under various conditions known to promote or prevent catabolite repression of the inducible beta-galactosidase system in this organism. Cultures were grown under these conditions in the presence of C(14)-glucose or C(14)-pyruvate. The products formed were assayed isotopically after separation on columns of silicic acid. Under conditions known to promote catabolite repression, glucose was degraded primarily to acetate and CO(2). When repression was turned off by anaerobic shock, glucose metabolism was characterized by the accumulation of ethyl alcohol in addition to acetate and CO(2). The results presented in this report indicate that oxidative decarboxylation of pyruvate may markedly affect the amount of energy that can be derived from glucose catabolism. In turn, the amount of energy derived from catabolic processes may play a key role in the mechanism of catabolite repression.

Acetates↗
PubMed1969

Molecular basis of transient repression of beta-galactosidase in Escherichia coli.

The molecular basis of transient repression of beta-galactosidase by glucose was examined. This repression acted only at the level of transcription. Apparently, it was not mediated by the I-gene product. Analysis of single cells in a culture subjected to transient repression showed that essentially all cells initially experienced repression and later became gradually resistant to repression.

Bacterial Proteins↗