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

Abstract

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.