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

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Abstract
In Streptomyces sp. 3022a, anthranilate synthetase is composed of 2 non-identical subunits. The major subunit (MW 72,000) converts chorismic acid to anthranilic acid, using NH3 as the source of the amino group. The smaller subunit (MW 28,000-29,000) confers on the enzyme the ability to use glutamine instead of NH3 as a substrate. The reactivity with glutamine reached its maximum at pH 7.2-7.6, but that with NH3 increased linearly through pH 9.0 without reaching a maximum. Activity was increased and stabilized by adding glutamine and MgCl2 to the buffer system. Both activites 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 did not increase antibiotic synthesis.