Characterization and Regulation of p-Aminobenzoic Acid Synthase from Streptomyces griseus

Abstract

P-Aminobenzoic acid synthase (PABA synthase) of S. griseus catalyses the conversion of chorismic acid to p-aminobenzoic acid (PABA), a precursor of the aromatic p-aminoacetophenone moiety of candicidin, a polyene macrolide antibiotic. This enzyme uses glutamine or ammonia as amino donors for PABA formation. Enzyme extracts converted [14C]chorismic acid to labeled PABA. PABA synthase was present in S. griseus IMRU 3570 only during the antibiotic producing phase. No detectable levels of the enzyme were found in cell-free extracts of nonproducing mutants of S. griseus obtained after UV mutagenesis. PABA synthase activity was found also in S. coelicolor var. aminophilus, producer of the polyene macrolide antibiotic fungimycin, but it was not present in extracts of several other streptomycetes that do not produce aromatic polyene macrolide antibiotics. PABA synthase (amidotranferase) activity was partially purified by DEAE-Bio-gel and Sephacryl S-200 filtrations. The esitmated MW was 50,000. PABA synthase was repressed by aromatic amino acids and PABA but not by anthranilic acid. Pi strongly repressed but did not inhibit PABA synthase activity.