Résumé
Spiramycin biosynthesis in Streptomyces ambofaciens was stimulated in the presence of valine or by sequential addition of some short-chain fatty acids to a culture medium containing an ammonium salt as source of nitrogen. Acetate kinase and acetyl-CoA carboxylase, enzymes that catalysed the formation of precursors of spiramycin biosynthesis (acetyl-CoA and malonyl-CoA), were detected during the active growth and antibiotic production phases. In this latter phase a higher level of acetyl-CoA carboxylase activity was observed with valine (1.02 μmol∙min
−1
∙mg protein
−1
) than with ammonium (0.05 μmol∙min
−1
∙mg protein
−1
) as nitrogen source, while the evolution and the level of acetate kinase activity were the same in both media. Successive addition of acetate and isobutyrate stimulated highly and weakly the acetyl-CoA carboxylase and acetate kinase activity, respectively.Key words: spiramycin, Streptomyces ambofaciens, valine.