Anthranilate Synthetase

Abstract

Abstract Anthranilate synthetase from Serratia marcescens was purified to homogeneity. Criteria for homogeneity were disc gel electrophoresis, sedimentation analysis, and immunodiffusion. During electrofocusing the enzyme was found to have an isoelectric pH of 4.6. Glutamine- and ammonia-dependent activities superimposed during electrofocusing. Glutamine-dependent activity showed a pH optimum of 7.6, while ammonia-dependent activity was optimal above pH 8.5, indicating that NH3 rather than NH4+ was involved in the reaction mechanism. The enzyme was sensitive to feedback inhibition by very low concentrations of l-tryptophan. The mercurial, p-chloromercuribenzoate, was found to be ineffective in desensitizing the enzyme to tryptophan inhibition. However, glutamine utilization was selectively and reversibly blocked. Chorismate enhanced this inactivation, while glutamine and a mixture of glutamine and chorismate were increasingly effective protective agents. A molecular weight of 140,000 was estimated from sucrose gradient centrifugation (7.6 S). The molecular weight on Sephadex gel filtration was 150,000.