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At least 163 records · Page 9Linked to original sources
PubMed2003

TRACP as an osteopontin phosphatase.

TRACP is synthesized as a latent proenzyme requiring proteolytic processing to attain maximal phosphatase activity. Excision of an exposed loop domain abolishes the interaction between the loop residue Asp146 and a ligand to the redox-sensitive iron of the active site, most likely Asn91, providing a mechanism for the enzyme repression. Both cathepsin K and L efficiently cleave in the loop domain and activate the latent enzyme, and we propose that cathepsin K acts as a physiological activator of TRACP in osteoclasts, whereas cathepsin L might fulfill a similar role in different types of macrophages. Considering the rather broad substrate specificity of TRACP, a tight regulation of its activity in the cell appears warranted. Besides proteolytic cleavage, the enzyme should need a specific local environment with a slightly acidic pH and reducing equivalents to keep the enzyme fully active. Cellular subcompartments where these required conditions prevail are potential subcellular site(s) of TRACP action. Of bone phosphoproteins shown to be substrates for TRACP, both osteopontin and bone sialoprotein are colocalized with TRACP in the resorption lacuna of the osteoclasts, and dephosphorylation of OPN impair its ability to promote adhesion as well as migration of osteoclasts in vitro. A role for TRACP as an osteopontin phosphatase in bone is therefore suggested. The expression of TRACP as well as OPN in other tissues with possible interactions between the two could suggest a more general function for TRACP as a regulator of OPN phosphorylation and bioactivity.

Acid Phosphatase↗
PubMed1989

Induction of repressible acid phosphatase by unsaturated fatty acid in Saccharomyces cerevisiae.

We studied the induction of acid phosphatase (APase) by fatty acids in Saccharomyces cerevisiae. S. cerevisiae has two types of APase: constitutive and repressible enzymes. The synthesis of the latter APase is normally derepressed by depletion of inorganic phosphate (Pi) in the incubation medium. Of the saturated and unsaturated fatty acids tested, linoleic, linolenic and arachidonic acids induced the synthesis of APase even in the presence of a high concentration of Pi, whereas palmitic, stearic and oleic acids did not. De novo protein synthesis but not stimulation of secretion of the enzyme was required for the induction. Genetic analyses using plasmids carrying the genes, PHO5 and PHO3, that code for repressible APase and constitutive APase, respectively, showed that linolenic acid induced the formation of repressible APase. Linolenic acid inhibited the uptake of exogenous 32Pi and simultaneously lowered the intracellular level of Pi. These circumstances indicate that linolenic acid-induced derepression of repressible APase is primarily caused by a fall in the intracellular level of Pi. However, cells that had been preincubated in the presence of a high concentration of Pi produced APase shortly after the addition of linolenic acid. It is, therefore, suggested that, as well as a normal regulatory mechanism for derepression of repressible APase, a mechanism independent of the external level of Pi participates in the induction of repressible APase by linolenic acid.

Acid Phosphatase↗
PubMed1986

Changes in glucose 6-phosphate dehydrogenase activity in developing embryonic chick skeletal muscle and spinal cord.

Glucose 6-phosphate dehydrogenase (G6PDH) activity was examined in the developing embryonic chick in brachial and lumbar spinal cord and pectoral and leg muscle. Enzyme activity was generally highest at the earliest stage examined, embryonic day 5. The developmental profiles for G6PDH activity in the two muscles were similar: a sharp initial decrease occurred between days 5 and 9, with relatively low levels present by day 18; peaks of G6PDH activity at days 12 and 16 were more prominent in leg muscle. Similar levels of G6PDH were also detected in spinal cord with the developmental profile in the brachial spinal cord resembling that seen in muscle. In lumbar spinal cord, initial G6PDH activity was lower than in brachial spinal cord; the developmental profile, however, resembled that seen in the brachial spinal cord, with an initial drop in enzyme activity seen between days 5 and 7. Neural regulation of G6PDH activity in mature muscle is believed to repress enzyme synthesis. The drop in G6PDH activity observed in embryonic spinal cord and muscle between days 5 and 9 coincides with the initiation of functional neuromuscular contacts. Hence, the normal regulation of G6PDH during embryonic development may involve the repression of G6PDH in spinal cord neurons and muscle, possibly effected by their interaction.

Animals↗
PubMed1982

Effects of anaerobiosis and nitrate on the expression of succinate dehydrogenase and enzymes associated with nitrogen metabolism in Klebsiella pneumoniae.

We have shown that the low histidase activity found in anaerobic, nitrogen-limited cultures of Klebsiella pneumoniae is due to repression of the right-hand hut operon. In addition, we have examined the effects of NO3- on the aerobic and anaerobic expression of catabolite- and NH4+-repressible enzymes in this organism. NO3- permitted anaerobic growth of K. pneumoniae in minimal medium containing histidine as the sole carbon source, and histidase and succinate dehydrogenase were derepressed during anaerobic growth in histidine/NO3- medium. Use of sucrose rather than histidine as the carbon source reversed the effects of NO3- and repressed histidase and succinate dehydrogenase activities. Anaerobic growth in sucrose/NO3- medium also uncoupled the expression of urease and glutamine synthetase.

Anaerobiosis↗
PubMed2005

Green gram husk--an inexpensive substrate for alkaline protease production by Bacillus sp. in solid-state fermentation.

Alkaline protease production under solid-state fermentation was investigated using isolated alkalophilic Bacillus sp. Among all agro-industrial waste material evaluated, green gram husk supported maximum protease production. Solid material particle size regulated the enzyme production and yield was improved with the supplementation of carbon and nitrogen sources to the solid medium. Optimum enzyme production was achieved with 1.5% maltose and 2.0% yeast extract with 371% increase than control. Glucose did not repressed enzyme production but inorganic nitrogen sources showed little negative impact. The physiological fermentation factors such as pH of the medium (pH 9.0), moisture content (140%), incubation time (60 h) and inoculum level played a vital role in alkaline protease production. The enzyme production was found to be associated with the growth of the bacterial culture.

Agriculture↗
PubMed1977

Escherichia coli mutants deficient in the aspartate and aromatic amino acid aminotransferases.

Two new mutations are described which, together, eliminate essentially all the aminotransferase activity required for de novo biosynthesis of tyrosine, phenylalanine, and aspartic acid in a K-12 strain of Escherichia coli. One mutation, designated tyrB, lies at about 80 min on the E. coli map and inactivates the "tyrosine-repressible" tyrosine/phenylalanine aminotransferase. The second mutation, aspC, maps at about 20 min and inactivates a nonrespressible aspartate aminotransferase that also has activity on the aromatic amino acids. In ilvE- strains, which lack the branched-chain amino acid aminotransferase, the presence of either the tyrosine-repressible aminotransferase or the aspartate aminotransferase is sufficient for growth in the absence of exogenous tyrosine, phenylalanine, or aspartate; the tyrosine-repressible enzyme is also active in leucine biosynthesis. The ilvE gene product alone can reverse a phenylalanine requirement. Biochemical studies on extracts of strains carrying combinations of these aminotransferase mutations confirm the existence of two distinct enzymes with overlapping specificities for the alpha-keto acid analogues of tyrosine, phenylalanine, and aspartate. These enzymes can be distinguished by electrophoretic mobilities, by kinetic parameters using various substrates, and by a difference in tyrosine repressibility. In extracts of an ilvE- tyrB- aspC- triple mutant, no aminotransferase activity for the alpha-keto acids of tyrosine, phenylalanine, or aspartate could be detected.

Aspartate Aminotransferases↗
PubMed1997

Identification and nitrogen regulation of the cyanase gene from the cyanobacteria Synechocystis sp. strain PCC 6803 and Synechococcus sp. strain PCC 7942.

An open reading frame (slr0899) on the genome of Synechocystis sp. strain PCC 6803 encodes a polypeptide of 149 amino acid residues, the sequence of which is 40% identical to that of cyanase from Escherichia coli. Introduction into a cyanase-deficient E. coli strain of a plasmid-borne slr0899 resulted in expression of low but significant activity of cyanase. Targeted interruption of a homolog of slr0899 from Synechococcus sp. strain PCC 7942, encoding a protein 77% identical to that encoded by slr0899, resulted in loss of cellular cyanase activity. These results indicated that slr0899 and its homolog in the strain PCC 7942 represent the cyanobacterial cyanase gene (designated cynS). While cynS of strain PCC 6803 is tightly clustered with the four putative molybdenum cofactor biosynthesis genes located downstream, cynS of strain PCC 7942 was found to be tightly clustered with the two genes located upstream, which encode proteins similar to the subunits of the cyanobacterial nitrate-nitrite transporter. In both strains, cynS was transcribed as a part of a large transcription unit and the transcription was negatively regulated by ammonium. Cyanase activity was low in ammonium-grown cells and was induced 7- to 13-fold by inhibition of ammonium fixation or by transfer of the cells to ammonium-free media. These findings indicated that cyanase is an ammonium-repressible enzyme in cyanobacteria, the expression of which is regulated at the level of transcription. Similar to other ammonium-repressible genes in cyanobacteria, expression of cynS required NtcA, a global nitrogen regulator of cyanobacteria.

Amino Acid Sequence↗
PubMed1995

Catabolite repression of induction of aldose reductase activity and utilization of mixed hemicellulosic sugars in Candida guilliermondii.

NADPH-dependent aldose reductase activity induced by D-xylose or L-arabinose was detected in cell-free extracts of Candida guilliermondii, but only negligible activities were observed if D-glucose served as carbon source. The induction of aldose reductase activity on mixed sugars was investigated under resting cell conditions. D-Glucose repressed enzyme induction by D-xylose or L-arabinose to varying degrees, and L-arabinose inhibited enzyme induction by D-xylose. During incubation in a mixture of D-xylose-D-glucose, glucose consumption by cells was fast and simultaneous with D-xylose utilization. Repression of D-xylose consumption by D-glucose was dependent on hexose initial concentration. L-arabinose consumption was poor when it was present as the only sugar and in a mixture with D-glucose; this pentose depletion occurred only when all hexose was consumed. When D-xylose and L-arabinose were present in a mixture, the consumption of both pentoses was reduced by the presence of the second sugar, although both sugars were consumed simultaneously by cells. The results show that induction of aldose reductase activity and D-xylose utilization by cells of Candida guilliermondii are under control of glucose repression.

Aldehyde Reductase↗
PubMed1970

Induction and repression of amidase enzymes in Aspergillus nidulans.

Aspergillus nidulans can grow on acetamide as both a carbon and nitrogen source and can also grow on formamide as a nitrogen source. Two distinct enzymes, an acetamidase and a formamidase, are produced. The control of the synthesis of these two enzymes in a wild-type strain was investigated. The formamidase is induced by acetamide and formamide and repressed by ammonia. The acetamidase is induced by formamide and acetamide, repressed by carbon metabolites derived from glucose and acetate, and repressed by ammonia. Repression of the acetamidase by ammonia depends on the carbon source; growth on glucose but not on acetate or acetamide allows repression to occur. The pattern of acetamidase repression is compared with that of histidine catabolic enzymes in various bacteria.

Amidohydrolases↗
PubMed2000

Isolation and characterization of beta-galactosidase from Lactobacillus crispatus.

beta-Galactosidase was isolated from the cell-free extracts of Lactobacillus crispatus strain ATCC 33820 and the effects of temperature, pH, sugars and monovalent and divalent cations on the activity of the enzyme were examined. L. crispatus produced the maximum amount of enzyme when grown in MRS medium containing galactose (as carbon source) at 37 degrees C and pH 6.5 for 2 d, addition of glucose repressing enzyme production. Addition of lactose to the growth medium containing galactose inhibited the enzyme synthesis. The enzyme was active between 20 and 60 degrees C and in the pH range of 4-9. However, the optimum enzyme activity was at 45 degrees C and pH 6.5. The enzyme was stable up to 45 degrees C when incubated at various temperatures for 15 min at pH 6.5. When the enzyme was exposed to various pH values at 45 degrees C for 1 h, it retained the original activity over the pH range of 6.0-7.0. Presence of divalent cations, such as Fe2+ and Mn2+, in the reaction mixture increased enzyme activity, whereas Zn2+ was inhibitory. The Km was 1.16 mmol/L for 2-nitrophenyl-beta-D-galactopyranose and 14.2 mmol/L for lactose.

Animals↗
PubMed1985

Regulation of expression of the ADE3 gene for yeast C1-tetrahydrofolate synthase, a trifunctional enzyme involved in one-carbon metabolism.

C1-THF (5,6,7,8-tetrahydrofolate) synthase is a trifunctional protein catalyzing the sequential reactions specified by the enzymes 10-formyl-THF synthetase (EC 6.3.4.3), 5,10-methenyl-THF cyclohydrolase (EC 3.5.4.9), and 5,10-methylene-THF dehydrogenase (EC 1.5.1.5). These three activities supply the activated one-carbon units required for the biosynthesis of purines, thymidylate, the amino acids histidine and methionine, the vitamin pantothenic acid, and the formyl group of mitochondrial fMet-tRNAfMet. Extracts of Saccharomyces cerevisiae whose growth is dependent on the three activities of C1-THF synthase contain 2-3 times the level of enzyme activity of extracts from cells grown under conditions where they are independent of this enzyme. Repression of C1-THF synthase activity requires the simultaneous presence of adenine, histidine, methionine, and pantothenic acid. Starvation of the cells for any one of these nutrients leads to derepression of the enzyme. Drug-induced folate starvation also leads to derepression of enzyme activity. The response to changing nutritional conditions occurs within 1 h and is due to changes in the steady-state concentration of C1-THF synthase enzyme, rather than to activation or deactivation of a pre-existing pool of enzyme. Determination of the amount of C1-THF synthase mRNA under the various growth conditions by an in vitro translation/immunoprecipitation assay indicates that regulation of the enzyme occurs predominantly at a pretranslational level since steady-state levels of C1-THF synthase mRNA are 2-3-fold higher in derepressed cells than in repressed cells.

Acetates↗
PubMed1997

Regulation of N-acetylglucosaminidase production in Candida albicans.

The N-acetylglucosaminidase of Candida albicans is a secreted hydrolytic enzyme that contributes to the yeast's virulence. There was a significant increase in the N-acetylglucosaminidase activity of C. albicans cells released from carbon starvation in medium containing N-acetylglucosamine. The increased enzyme activity in N-acetylglucosamine-grown cells correlated with increased transcription of the HEX1 gene, which encodes C. albicans N-acetylglucosaminidase. In contrast, glucose repressed HEX1 transcription, and glucose-grown cells had on average 94-fold lower N-acetylglucosaminidase activities than did N-acetylglucosamine-grown cells. N-acetylglucosaminidase induction in cells grown on N-acetylglucosamine was also repressed by fructose, mannose or galactose, although to a lesser extent than by glucose, and sucrose repressed enzyme production by only 10%. Eighty-eight percent of the enzyme in N-acetylglucosamine-grown cells was localised in the periplasm, and after incubation for 5 h, 30 or 70% of the total enzyme activity was secreted into the medium by yeast or mycelial cells, respectively. The cellular location of the enzyme and the regulation of production by the carbon source indicate a scavenging role for C. albicans N-acetylglucosaminidase.

Acetylglucosamine↗
PubMed1984

The in vivo effect of benzamide and phenobarbital on liver enzymes: poly(ADP-ribose) polymerase, cytochrome P-450, styrene oxide hydrolase, cholesterol oxide hydrolase, glutathione S-transferase and UDP-glucuronyl transferase.

Rats fed a synthetic diet containing 0.25% benzamide, 0.1% phenobarbital, separately or in combination, for two weeks showed a significant augmentation in the activity of nuclear poly(ADP-ribose) polymerase as well as changes in various nuclear, microsomal and cytosolic liver enzymes involved in the metabolism of xenobiotics. A selective depression of microsomal styrene oxide hydrolase activity by benzamide feeding, and a contrasting augmentation by phenobarbital, were confirmed by immunological titration of the enzyme-protein content suggesting actual enzyme repression and induction. The NAD content of these livers is not altered significantly as a result of benzamide and phenobarbital feeding, indicating that the changes in enzymes are not a result of non-specific toxic effects.

3-Hydroxysteroid Dehydrogenases↗
PubMed1976

The existence of three types of acetohydroxy acid synthetase in an isoleucine-requiring mutant of Aerobacter aerogenes.

The synthesis of the three types of acetolactate synthase (EC 4.1.3.18) which are responsible for the biosynthesis os isoleucine and valine, was observed in Aerobacter aerogenes I-12, an isoleucine-requiring mutant, when grown on the four kinds of media. When the cells were grown on isoleucine-rich medium, acetolactate synthase sensitive to feedback inhibition and having an optimum pH at 8.0 was formed. By increasing the amount of potassium phosphate in the medium, the catabolite repression of the enzyme having an optimum pH at 6.0 and which is insensitive to feedback inhibition, was released. In contrast, acetolactate synthase having an optimum pH at 8.0 and insensitive to feedback inhibition was formd when isoleucine was limited, irrespective of phosphate concentrations. Two insensitive enzymes were not regulated by isoleucine, leucine and valine, although sensitive pH 8.0 enzyme was repressed by them. Thus, it may be assumed that the synthesis of insensitive pH 8.0 enzyme were repressed by limiting the amount of isoleucine is still open.

Acetolactate Synthase↗
PubMed1986

Antibiotic resistance of Pseudomonas species.

Pseudomonas species are highly versatile organisms with genetic and physiologic capabilities that allow them to flourish in environments hostile to most pathogenic bacteria. Within the lung of the patient with cystic fibrosis, exposed to a number of antimicrobial agents, highly resistant clones of Pseudomonas are selected. These may have acquired plasmid-mediated genes encoding a variety of beta-lactamases or aminoglycoside modifying enzymes. Frequently these resistance determinants are on transposable elements, facilitating their dissemination among the population of bacteria. Mutations in chromosomal genes can also occur, resulting in constitutive expression of normally repressed enzymes, such as the chromosomal cephalosporinase of Pseudomonas aeruginosa or Pseudomonas cepacia. These enzymes may confer resistance to the expanded-spectrum beta-lactam drugs. Decreased cellular permeability to the beta-lactams and the aminoglycosides also results in clinically significant antibiotic resistance. The development of new drugs with anti-Pseudomonas activity, beta-lactam agents and the quinolones, has improved the potential for effective chemotherapy but has not surpassed the potential of the organisms to develop resistance.

Aminoglycosides↗
PubMed1989

Pyrimidine, purine and nitrogen control of cytosine deaminase synthesis in Escherichia coli K 12. Involvement of the glnLG and purR genes in the regulation of codA expression.

Cytosine deaminase, encoded by the codA gene in Escherichia coli catalyzes the deamination of cytosine to uracil and ammonia. Regulation of codA expression was studied by determining the level of cytosine deaminase in E. coli K12 grown in various defined media. Addition of either pyrimidine or purine nucleobases to the growth medium caused repressed enzyme levels, whereas growth on a poor nitrogen source such as proline resulted in derepression of cytosine deaminase synthesis. Derepression of codA expression was induced by starvation for either uracil or cytosine nucleotides. Nitrogen control was found to be mediated by the glnLG gene products, and purine repression required a functional purR gene product. Studies with strains harbouring multiple mutations affecting both pyrimidine, purine and nitrogen control revealed that the overall regulation of cytosine deaminase synthesis by the different metabolites is cumulative.

Culture Media↗