A Steady‐State Kinetic Investigation of the Reaction Mechanism of the Tryptophan Synthetase of Escherichia coli

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.