A steady-state kinetic investigation of the reaction mechanism of the tryptophan synthetase of Escherichia coli.

Abstract

The initial rate of glyceraldehyde‐P formation catalyzed by the tryptophan synthetase of Escherichia coli from indole‐3‐glycerol‐P has been measured as a function of the concentrations of indole‐glycerol‐P, serine, tryptophan, and indole. The conversion of indole‐glycerol‐P to indole and glyceraldehyde‐P is proposed to proceed by the ordered sequential release from the enzyme of indole followed by glyceraldehyde‐P. Tryptophan does not appreciably inhibit this reaction. Tryptophan formation is proposed to occur by the random sequential addition of serine and indole‐glycerol‐P to the enzyme. Tryptophan is a product inhibitor of the reaction, apparently combining with the free enzyme and also forming an enzyme‐(indole‐glycerol‐P)‐tryptophan deadend complex. Indole inhibits non‐competitively with respect to both indole‐glycerol‐P and serine, and is proposed to combine with the free enzyme and with the enzyme having bound indole‐glycerol‐P, serine, or both substrates. The implications of the results for the catalytic center and subunit structure of the enzyme are discussed.