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

TLDR: The results show that 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, and the implications for the catalytic center and subunit structure of the enzyme are discussed.

Abstract: 1 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. 2 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. 3 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. 4 The implications of the results for the catalytic center and subunit structure of the enzyme are discussed.