Characterization and regulation of anthranilate synthetase from a chloramphenicol-producing streptomycete

In Streptomyces sp. 3022a, anthranilate synthetase is composed of two non-identical subunits. The major subunit (molecular weight, 72,000) converts chorismic acid to anthranilic acid, using ammonia as the source of the amino group. The smaller subunit (molecular weight 28,000 to 29,000) confers on the enzyme the ability to use glutamine instead of ammonia as a substrate. In this study, reactivity with glutamine reached its maximum at pH 7.2 to 7.6, whereas that with ammonia increased linearly through pH 9.0 without reaching a maximum. Activity was increased and stabilized by adding glutamine and magnesium chloride to the buffer system. Both activities of the enzyme were inhibited by anthranilic acid and by tryptophan. Synthesis was repressed by histidine, anthranilic acid, tryptophan, and p-aminobenzoic acid. When activity was repressed by anthranilic acid and by tryptophan, there was a concomitant increase in the activity of arylamine synthetase, an enzyme involved in chloramphenicol production. Stimulating arylamine synthetase, however, did not increase antibiotic synthesis.