The Role of Pyridoxal Phosphate in the Aldolytic Activity of Tryptophan Synthetase from Neurospora Crassa.

The formation of tryptophan (Reactions 1 and 2) requires the coenzyme pyridoxal phosphate. According to the proposed mechanism of action of pyridoxal enzymes (3, 4), the aldolyticl activity of tryptophan synthetase (Reactions 3f and 3r) would not be expected to require pyridoxal-P as a coenzyme; yet DeMoss and Bonner (7) reported that the Reaction 3f activity of a mutationally altered tryptophan synthetase of Neurospora crassa was stimulated by the coenzyme. We have used pyridoxal-P and several pyridoxal-P analogues to determine which groups of the coenzyme play a role in Reaction 3f activity of normal and mutationally altered tryptophan synthetase.