Ammonium ions repress δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine synthetase in Streptomyces clavuligerus NRRL 3585

1989 ◽  
Vol 35 (3) ◽  
pp. 399-402 ◽  
Author(s):  
Jinyou Zhang ◽  
Saul Wolfe ◽  
Arnold L. Demain
Keyword(s):  
Streptomyces Clavuligerus ◽  
Defined Medium ◽  
Antibiotic Biosynthesis ◽  
Chemically Defined Medium ◽  
Ammonium Ions ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Negative Effect ◽  
Major Factors ◽  
Rate Limiting

Production of cephems (predominantly cephamycin C) by Streptomyces clavuligerus grown in chemically defined medium supplemented with 120 mM NH4Cl was sharply reduced. This concentration of ammonium ions in the medium repressed δ-(L-α-aminoadipyl)-L-cysteinyl-D-valine (ACV) synthetase formation by about 75%. Of the other cephalosporin synthases, cyclase was repressed by 70%, expandase by 50%, and epimerase only to a very small extent. Inhibition of the action of ACV synthetase was only slight in the presence of 100 mM NH4Cl. Repression of ACV synthetase, cyclase, and expandase appears to be the major factors contributing to the negative effect of ammonium on S. clavuligerus NRRL 3585. ACV synthetase is probably the rate-limiting step of cephalosporin biosynthesis in this strain.Key words: β-lactam biosynthesis, antibiotic biosynthesis, cephalosporins, Streptomyces clavuligerus, ACV synthetase.

Ammonium repression of cephalosporin production by Streptomyces clavuligerus

1985 ◽  
Vol 31 (8) ◽  
pp. 736-743 ◽  
Author(s):  
Alfredo F. Braña ◽  
Saul Wolfe ◽  
Arnold L. Demain
Keyword(s):  
Specific Activity ◽  
Relative Proportion ◽  
Streptomyces Clavuligerus ◽  
Defined Medium ◽  
Inhibitory Effects ◽  
Rate Limiting Step ◽  
Deacetoxycephalosporin C Synthetase ◽  
Isopenicillin N Synthetase ◽  
Rate Limiting ◽  
Isopenicillin N

Production of β-lactam antibiotics took place during growth of Streptomyces clavuligerus in chemically defined medium. The specific activities of isopenicillin N synthetase ("cyclase"), isopenicillin N epimerase, and deacetoxycephalosporin C synthetase ("expandase") increased during the exponential phase of growth. Specific cephalosporin productivity during fermentation followed a similar pattern, reaching a maximum near the end of the growth phase and decaying rapidly in the stationary phase. Ammonium chloride depressed cephalosporin production, presumably as a result of repression of cyclase and expandase formation, but not of epimerase. No inhibitory effects on enzyme activity by ammonium were found. Addition of tribasic magnesium phosphate [Mg3(PO4)2∙8H2O] prevented the repression of cyclase and markedly stimulated cephalosporin production. Cephamycin C and, in smaller amounts, O-carbamoyldeacetylcephalosporin C were the only cephalosporins detected. Growth with ammonium resulted in lower titers of both compounds, and did not change the relative proportion of each. The correlation found between cephalosporin productivity and cyclase specific activity in different media suggests that formation of this enzyme may be the rate-limiting step in the pathway.

Ornithine Decarboxylase Activity in Cultured Endothelial Cells Stimulated by Serum, Thrombin and Serotonin

1978 ◽  
Vol 39 (02) ◽  
pp. 496-503 ◽  
Author(s):  
P A D’Amore ◽  
H B Hechtman ◽  
D Shepro
Keyword(s):  
Endothelial Cells ◽  
Ornithine Decarboxylase ◽  
Decarboxylase Activity ◽  
Aortic Endothelial Cells ◽  
Ornithine Decarboxylase Activity ◽  
Rate Limiting Step ◽  
Bovine Aortic Endothelial Cells ◽  
Limiting Step ◽  
Rate Limiting ◽  
Serum Serotonin

SummaryOrnithine decarboxylase (ODC) activity, the rate-limiting step in the synthesis of polyamines, can be demonstrated in cultured, bovine, aortic endothelial cells (EC). Serum, serotonin and thrombin produce a rise in ODC activity. The serotonin-induced ODC activity is significantly blocked by imipramine (10-5 M) or Lilly 11 0140 (10-6M). Preincubation of EC with these blockers together almost completely depresses the 5-HT-stimulated ODC activity. These observations suggest a manner by which platelets may maintain EC structural and metabolic soundness.

Dynamics of hepatic and peripheral insulin effects suggest common rate-limiting step in vivo

Diabetes ◽  
1993 ◽  
Vol 42 (2) ◽  
pp. 296-306 ◽  
Author(s):  
D. C. Bradley ◽  
R. A. Poulin ◽  
R. N. Bergman
Keyword(s):  
Rate Limiting Step ◽  
Limiting Step ◽  
Rate Limiting

Kinetics of cyclization of S-ethoxycarbonylmethylisothiouronium chloride to 2-imino-4-thiazolidone

1979 ◽  
Vol 44 (3) ◽  
pp. 912-917 ◽  
Author(s):  
Vladimír Macháček ◽  
Said A. El-bahai ◽  
Vojeslav Štěrba
Keyword(s):  
Hydrochloric Acid ◽  
Dilute Hydrochloric Acid ◽  
Base Catalysis ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Kinetics Of Formation ◽  
Acid Catalyzed ◽  
Rate Limiting ◽  
Kinetics Of

Kinetics of formation of 2-imino-4-thiazolidone from S-ethoxycarbonylmethylisothiouronium chloride has been studied in aqueous buffers and dilute hydrochloric acid. The reaction is subject to general base catalysis, the β value being 0.65. Its rate limiting step consists in acid-catalyzed splitting off of ethoxide ion from dipolar tetrahedral intermediate. At pH < 2 formation of this intermediate becomes rate-limiting; rate constant of its formation is 2 . 104 s-1.

Kinetics and mechanism of cyclization of N-(2-methoxycarbonylphenyl)-N’-methylsulphonamide to 3-methyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide

1991 ◽  
Vol 56 (8) ◽  
pp. 1701-1710 ◽  
Author(s):  
Jaromír Kaválek ◽  
Vladimír Macháček ◽  
Miloš Sedlák ◽  
Vojeslav Štěrba
Keyword(s):  
Potassium Hydroxide ◽  
Acid Catalysis ◽  
Potassium Hydroxide Solution ◽  
Hydroxide Solution ◽  
General Base ◽  
Rate Limiting Step ◽  
Limiting Step ◽  
Cyclization Kinetics ◽  
Rate Limiting ◽  
Kinetics Of

The cyclization kinetics of N-(2-methylcarbonylphenyl)-N’-methylsulfonamide (IIb) into 3-methyl-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide (Ib) has been studied in ethanolamine, morpholine, and butylamine buffers and in potassium hydroxide solution. The cyclization is subject to general base and general acid catalysis. The value of the Bronsted coefficient β is about 0.1, which indicates that splitting off of the proton from negatively charged tetrahedral intermediate represents the rate-limiting and thermodynamically favourable step. In the solutions of potassium hydroxide the cyclization of dianion of the starting ester IIb probably becomes the rate-limiting step.

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