Stereochemistry and mechanism of a new single-turnover, half-transamination reaction catalyzed by the tryptophan synthase alpha 2 beta 2 complex.
Tryptophan synthase is a versatile enzyme that catalyzes a wide variety of pyridoxal phosphate dependent reactions that are also catalyzed in model systems. These include beta-replacement, beta-elimination, racemization, and transamination reactions. We now show that the apo-alpha 2 beta 2 complex of tryptophan synthase will bind two unnatural substrates, pyridoxamine phosphate and indole-3-pyruvic acid, and will convert them by a single-turnover, half-transamination reaction to pyridoxal phosphate and L-tryptophan, the natural coenzyme and a natural product, respectively. This enzyme-catalyzed reaction is more rapid and more stereospecific than an analogous model reaction. The pro-S 4'-methylene proton of pyridoxamine phosphate is removed during the reaction, and the product is primarily L-tryptophan. We conclude that pyridoxal phosphate enzymes may be able to catalyze some unnatural reactions involving bound reactants and bound coenzyme since the coenzyme itself has the intrinsic ability to promote a variety of reactions.
D004926:Escherichia coli / Q000201:enzymology; D007211:Indoles / Q000378:metabolism*; D007700:Kinetics; D046911:Macromolecular Substances; D011485:Protein Binding; D011733:Pyridoxamine / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000378:metabolism; D013053:Spectrophotometry; D014316:Tritium; D014367:Tryptophan Synthase / Q000378:metabolism*
D007211:Indoles; D046911:Macromolecular Substances; D014316:Tritium; C008122:indol-3-yl pyruvic acid; D011733:Pyridoxamine; D014367:Tryptophan Synthase; C010627:pyridoxamine phosphate