A Steady-State Kinetic Investigation of the Reaction Mechanism of the Tryptophan Synthase of <em>Escherichia coli</em>.

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 dead-end 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. [ABSTRACT FROM AUTHOR]