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PubMed1983

Control of catechol meta-cleavage pathway in Alcaligenes eutrophus.

Alcaligenes eutrophus 335 (ATCC 17697) metabolizes phenol and p-cresol via a catechol meta-cleavage pathway. Studies with mutant strains, each defective in an enzyme of the pathway, showed that the six enzymes assayed are induced by the primary substrate. Studies with a putative polarity mutant defective in the expression of aldehyde dehydrogenase suggested that the structural genes encoding this and subsequent enzymes of the pathway exist in the same operon. From studies with mutant strains that constitutively synthesize catechol 2,3-oxygenase and subsequent enzymes and from the coordination of repression of these enzymes by p-toluate, benzoate, and acetate, it is proposed the catechol 2,3-oxygenase structural gene is situated in this operon (2,3-oxygenase operon). Studies with regulatory mutant strains suggest that the 2,3-oxygenase operon is under negative control.

Alcaligenes↗
PubMedDate not supplied

Influence of carbon and nitrogen sources on arginine biosynthesis in Mycobacterium smegmatis ATCC 14468.

Arginine biosynthesis and its regulation by the presence of different carbon and nitrogen sources in the growth medium of Mycobacterium smegmatis was studied. Replacement of glycerol by glucose and fructose increased the activities of acetylglutamate kinase, acetylornithinase and ornithine transcarbamylase and the enzyme activities of the arginine biosynthetic pathway. The presence of succinate, fumarate, pyruvate or acetate in the growth medium (replacement for citrate) also increased these enzyme activities. However, when glutamate or glutamine was used as nitrogen source in place of asparagine, the enzyme activities decreased. The presence of ornithine or arginine in the growth medium repressed these enzyme activities, though the degree of repression was slight. The phenomenon of repression by arginine and ornithine was confirmed by dialysis experiments. Arginine inhibited the ornithine transcarbamylase activity from cells grown with asparagine as nitrogen source, but activated it when the cells were grown with arginine. Thus, in addition to the weak transcriptional control of arginine biosynthetic enzymes, feedback regulation of ornithine transcarbamylase by arginine also regulated arginine biosynthesis in M. smegmatis grown with asparagine as nitrogen source.

Arginine↗
PubMed1965

Repression of lambda-Associated Enzyme Synthesis After lambda(vir) Superinfection of Lysogenic Hosts.

Lisio, Arnold L. (National Institutes of Health, Bethesda, Md.), and Arthur Weissbach. Repression of lambda-associated enzyme synthesis after lambda(vir) superinfection of lysogenic hosts. J. Bacteriol. 90:661-666. 1965.-Phage lambda(vir) is a multiple mutant of lambda which is capable of overcoming the immunity of a host lysogenic for lambda, and initiating normal vegetative replication of the superinfecting phage genome. Superinfection of Escherichia coli K-112 (lambda(22)) with lambda(vir) results in a normal phage yield, lysis time, and H(3)-thymine incorporation compared with infection of the sensitive host, K-112 (S). However, the production of the lambda phage-specific early protein, lambda-exonuclease, after superinfection of E. coli K-112 (lambda(22)) with lambda(vir) is only 25 to 50% of that obtained from corresponding infection of a nonlysogenic host, E. coli K-112 (S). This repression of lambda-exonuclease synthesis is dependent on the C(1) cistron of the prophage and is overcome if the lysogenic host cells are induced prior to superinfection. The data are interpreted as evidence for partial repression of lambda(vir) by the host immunity.

Journal Article↗
PubMed1969

Repression-dependent alteration of an arginine enzyme in Escherichia coli.

Treatment of susceptible Escherichia coli K12 derivatives with 0.4 M Mg(++) at 37 degrees , potentiated by L-arginine or L-canavanine, leads to alteration of acetylornithine delta-transaminase. The alteration, obtained in the absence of protein synthesis and reversible at 0 or 37 degrees , is manifested in extracts by lowered activity and modified substrate affinity behavior of the enzyme without gross changes in sedimentation properties. Cells grown under arginine repression are susceptible to the treatment; cells grown under genetic or steady-state physiological derepression are not. Transaminase synthesized during early derepression can be altered, although to progressively diminishing extents. Enzyme formed under steady-state derepression becomes alterable following transition to repression. The Mg(++) -dependent alteration can be thought to arise while the enzyme, arginine (or canavanine), and aporepressor are in contact, and to reflect a physiological process such as the participation of the enzyme in the repressive complex.

Arginine↗
PubMed1974

First enzyme of histidine biosynthesis and repression control of histidyl-transfer ribonucleic acid synthetase of Salmonella typhimurium.

The regulation of formation of histidyl-transfer ribonucleic acid (tRNA) synthetase was examined in strains of Salmonella typhimurium. When the first of the histidine-forming enzymes was wild type, the presence of 2-thiazolealanine in the growth medium prevented repression of histidyl-tRNA synthetase formation elicited by the addition of 1, 2, 4-triazole-3-alanine to these cultures. Conversely, thiazolealanine had no effect on repression of histidyl-tRNA synthetase formation by triazolealanine in hisG mutant strains. These data suggest a relationship between the control of histidyl-tRNA synthetase formation and the functional state of the histidine operon.

Amino Acids↗
PubMed1962

Metabolic control of beta-glucosidase synthesis in yeast.

MacQuillan, Anthony M. (University of Wisconsin, Madison) and Harlyn O. Halvorson. Metabolic control of beta-glucosidase synthesis in yeast. J. Bacteriol. 84:23-30. 1962-The hybrid Saccharomyces fragilis x S. dobzhanskii produced a constitutive beta-glucosidase when grown in succinate synthetic medium. Upon addition of beta-glucosides, thio-beta-glucosides, or low concentrations of glucose, a further induction of enzyme synthesis was observed. Studies with other sugars revealed some specificity in response to hexose induction. Phenyl-thio-beta-d-glucoside did not affect constitutive synthesis nor induction by glucosides, thio-glucosides, or glucose. Repression of beta-glucosidase synthesis is brought about by high concentrations of glucose and other carbon compounds. Preinduction does not confer resistance to catabolic repression of enzyme synthesis; this leads to the conclusion that two sites of control for beta-glucosidase synthesis are present in yeast. Multiplicity of control is further suggested from: (i) the properties of the inducing system; (ii) semiconstitutive nature of enzyme synthesis; (iii) the repression of constitutive synthesis by glucose; (iv) the elevated derepressed rates of enzyme synthesis after glucose inhibition; and (v) the selection of a family of low constitutive mutants with variable inducibility.

Cellulases↗
PubMed1994

Production and partial characterization of an endopolygalacturonase from Saccharomyces cerevisiae.

Saccharomyces cerevisiae CECT1389 secreted an extracellular endopolygalacturonase (EC 3.2.1.15) when grown in shake flasks in medium containing galactose alone, or either galactose and polygalacturonic acid or galactose and galacturonic acid as the carbon sources. The synthesis of the enzyme was repressed by glucose and by high oxygen tensions. The enzyme was partially purified by gel exclusion chromatography over Sephacryl S-200, where it showed an apparent molecular mass of 39 kDa; the value determined by high-performance liquid chromatography (HPLC) was 65 kDa. The optimal temperature and pH for enzyme activity were 45 degrees C and 5.5, respectively. The Km and Vmax values for polygalacturonic acid were 4.7 mg.mL-1 and 6.4 nmol.mL-1.min-1. The Ki for HgCl2 was 6.8 x 10(-5) M. The enzyme exhibited an endo-splitting mechanism as deduced from viscosimetry experiments as well as from an HPLC study of the end products.

Enzyme Inhibitors↗
PubMed1975

Activity of liver fructose diphosphatase from chick embryos treated with aminoguanidine sulfate.

Injection of chick embryos with aminoguanidine sulfate (AGS) on the fourth day of incubation resulted in a decreased specific activity of liver fructose diphosphatase (FDPase) prior to hatch time. This decreased FDPase specific activity was found to be the consequence of increased levels of an enzyme inhibitor (adenosin 5'-monophosphate) rather than a specific repression of enzyme synthesis.

Adenosine Monophosphate↗
PubMed1979

Insulin resistance in obesity: a critical analysis at enzyme level. A review.

Based on the consideration that insulin does not act directly on metabolic processes but affects membrane carriers and key-enzymes that regulate metabolic pathways, determination of insulin responsiveness of the various key-enzymes is suggested as a very appropriate method for studying insulin resistance. Insulin resistance, as it occurs in obese or obese-diabetic humans and animals, is most often associated with hyperinsulinemia, and is characterized not only by increased activity of key-enzymes of pathways known to be stimulated by insulin (glycolysis, lipogenesis), with the possible exception of glycogen synthesis, but also by a trend towards increased activity of key-enzymes of 'catabolic pathways', normally depressed by insulin. In the adipose tissue there is a normal-to-enhanced basal lipolysis, which in man would result from the prevalence of the active over the inactive form of triacylglycerol lipase. In muscle, the increased amino-acid release that can be inferred from the elevated blood level of both alanine and branched-chain amino acids suggests an enhanced proteolysis. In liver, there is an elevation in the activity of the key gluconeogenic enzymes, which forms the basis of the augmented gluconeogenesis. In both muscle and liver, phosphorylase is also elevated with no change in glycogen synthase. Therefore, insulin resistance seems to consist of the failure of insulin to depress the key-enzymes of catabolic pathways. Possible resistance of glycogen synthetase, which might account for decreased glucose utilization in muscle, may be due to the opposing effects of the phosphorylation process on glycogen synthetase and phosphorylase, implying that activation of phosphorylase (which occurs in obesity) entails inhibition of the synthetase. The fact that insulin insensitivity concerns only the 'catabolic' but not most 'anabolic' pathways makes it unlikely that the unresponsiveness is due to a reduction in insulin receptors or increase in insulin degradation. Since resistance to insulin is shown by enzymes regulated by such different mechanisms as induction-repression (gluconeogenic enzymes), covalent modifications (lipase, phosphorylase), and changes in lysosome stability (lysosomal proteases responsible for proteolysis, a single basic mechanism for explaining insulin insensitivity cannot be envisaged at present.

Adipose Tissue↗
PubMed1977

Biosynthesis of a alpha-amylase and protease by Streptomyces olivaceus 142. III. Some aspects of alpha-amylase induction.

The induction of alpha-amylase in Streptomyces olivaceus 142 depends on the phase of growth of culture and the nature of the carbon sources upon which the cells were grown prior to exposure to inducer. The most susceptible to induction are cells from the initial hours of growth and glycerol -- grown cells. Reduction in the susceptibility of cells to alpha-amylase induction is probably a result of catabolic repression.

Amylases↗
PubMed1980

[Genetico-biochemical study of the acid phosphatases of Saccharomyces cerevisiae yeasts. X. Analysis of mutations arising in gene acp3].

Mutations leading to decrease or absence of orthophosphate-repressible acid phosphatase activity have been studied. It is shown that these mutations can arise in three genes: acp1, acp2 and acp3, which are not linked. Genes acp1 and acp2 have been studied previously; the existence of the gene acp3 is demonstrated in this paper. It is established that all mutations in the acp3 gene are recessive, are leaky and epistatic to the constitutive mutations in all known regulatory genes for acid phosphatase II synthesis - acp4, acp80, acp81, acp82, acp83, and acp84. The gene acp3 is not linked with these regulatory genes, but it is closely linked with the structural gene for constitutive acid phosphatase - pho1 (D=0.33+/-0.20 cM). The pho1 gene has been recently located on the right arm of chromosome II on the left of the gene lys2. Mutations lacking activity of constitutive and repressible acid phosphatases simultaneously have been found. It is shown that these mutations are allelic to mutations in the gene acp3 and pho1 simultaneously. Two hypotheses are proposed about the role of the gene acp3: the gene controls the positive factor for the repressible acid phosphatase synthesis or the structure of the enzyme.

Acid Phosphatase↗
PubMed1989

Production of cell wall-degrading enzymes by Aspergillus nidulans: a model system for fungal pathogenesis of plants.

The cell wall-degrading enzymes polygalacturonase and pectate lyase have been suggested to be crucial for penetration and colonization of plant tissues by some fungal pathogens. We have found that Aspergillus nidulans (= Emericella nidulans), a saprophytic Ascomycete, produces levels of these enzymes equal to those produced by soft-rotting Erwinia species. Induction of polygacturonase and pectate lyase in A. nidulans requires substrate and is completely repressed by glucose. Surprisingly, inoculation of excised plant tissues with A. nidulans conidia leads to formation of necrotic, water-soaked lesions within which the organism sporulates. Thus, A. nidulans has phytopathogenic potential. The release of glucose and other sugars from wounded tissues may repress pectolytic enzyme production and limit disease development. Therefore, we tested creA204, a mutation that relieves glucose repression of some A. nidulans carbon utilization enzymes, for its effect on production of pectolytic enzymes. creA204 failed to relieve catabolite repression of polygalacturonase or pectate lyase and had no effect on disease severity.

Aspergillus nidulans↗
PubMed1981

[Influence of alcohol lipotropic agents on biosynthesis and repression of secreted alkaline phosphatase in Escherichia coli].

Preincubation of cells in the presence of 4% ethanol accompanied by an increase of non-saturated cis-vaccenic acid content was shown to promote synthesis of alkaline phosphatase. Preincubation of cells in 0.1% hexanol reducing the level of this acid, on the contrary, leads to partial repression of the enzyme synthesis; the lag-phase of repression in the cells with a raised content of non-saturated cis-vaccenic acid and, consequently, with a greater fluidity of lipids was also shown to be reduced. Conversely, the reduction of lipid membrane fluidity on ethanol addition simultaneously with the repressing metabolite ortho-phosphate extends the lag-phase of repression and removes it partially during cell cultivation in the presence of ortho-phosphate. The impact of lipid composition variations on the synthesis and repression of alkaline phosphatase is discussed.

Alcohols↗
PubMed1982

Purification and identification of inactive forms of repressible and constitutive acid phosphatase in yeast.

Acid phosphatase (EC 3.1.3.2, orthophosphoric-monoester phosphohydrolase, (acid optimum) from the budding yeast Saccharomyces cerevisiae was purified from repressed and derepressed cells. Without Triton X-100 in the extraction buffer only the constitutive or repressible active enzyme eluted from a Sepharose CL-6B column, the last step of the purification procedure. When Triton X-100 was included in the extraction buffer, an additional protein peak eluted prior to the active acid phosphatase. The material from this new peak, a glycoprotein, had no acid phosphatase activity but cross-reacted with antibodies raised against repressible acid phosphate. The tryptic fingerprints of the inactive proteins are very similar to the ones of the corresponding active enzymes. We conclude that this new glycoprotein represents an inactive form of repressible and constitutive acid phosphatase. The fact that inactive acid phosphatase can be recovered only in the presence of Triton X-100 indicates that it is membrane-bound.

Acid Phosphatase↗