The incorporation of uniformly 14C-labeled compounds into the streptothricin-type antibiotic nourseothricin was studied with a strain of Streptomyces noursei JA 3890b. 6.5 % of radioactivity from U-14C-L-arginine was incorporated into the antibiotic, while glutamic acid, aspartic acid, alanine, proline, glycine and leucine displayed much lower incorporations. Furthermore, 95 % of the activity incorporated from arginine was located in the streptolidine moiety supporting the suggestion that this subunit of streptothricin antibiotics is formed via the dehydroarginine pathway.

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The biosynthesis of nourseothricin, a streptothricin type antibiotic, is strongly stimulated by o-aminobenzoic acid in cultures of S. noursei J A 3890b. o-Aminobenzoic acid (OAB) was shown t o interfere with the amino acid metabolism and t o influence last not least. the efficacy of t,he precursor supplying system in the antibiotic biosynthesis. Thus, mycelium cultivated in presence of OAB (7.5 mM) exhibits strongly increased activities of N14DPspecific glutamate dehydrogenase. Simultaneously, this effector prevents the induction of alanine dehydrogenase in productive cultures suggesting that' an enhanced formatiori of alanine interferes with antibiotic biosynthesis. Insignificant variations of further enzymic activities, a.q. of transaminases, of phosphoenolpyruvate carboxylase and of enzymes of the tricarboxylic a.cid cycle were observed. Furthermore, the possible role of o-aminobenzoic acid as an effector of metabolite transport systems or of energy metabolism is discussed.

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