Ozonization of the tryptophyl residue in tryptophanase

Abstract

Tryptophanase of Escherichia coli was inactivated by ozonization in aqueous solution in a time-dependent fashion following pseudo-first order kinetics. Upon ozonization of the apoenzyme, the absorption peak of the tryptophyl residue at 280 nm gradually decreased concomitant with an appearance of a new peak at 320 nm indicating conversion of the tryptophyl residue to N′-formylkynurenine. The spectrophotometric titration of the coenzyme binding to the enzyme protein at 430 nm indicated that the dissociation constant for the coenzyme was almost 100 times increased upon ozonization presumably by weakening the interaction between the coenzyme and the indole moiety of the tryptophyl residue in the enzyme protein.