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.
- Research Organization:
- National Institute of Diabetes, Bethesda, MD
- OSTI ID:
- 6529314
- Journal Information:
- Biochemistry; (United States), Journal Name: Biochemistry; (United States) Vol. 2; ISSN BICHA
- Country of Publication:
- United States
- Language:
- English
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59 BASIC BIOLOGICAL SCIENCES
AMINO ACIDS
AROMATICS
AZAARENES
AZINES
AZOLES
BACTERIA
BIOCHEMICAL REACTION KINETICS
CARBOXYLIC ACIDS
CATALYSIS
ENZYMES
ESCHERICHIA COLI
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
HYDROLASES
INDOLES
KINETICS
LABELLED COMPOUNDS
MICROORGANISMS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PYRIDINES
PYRROLES
REACTION KINETICS
SPECTROPHOTOMETRY
TRITIUM COMPOUNDS
TRYPTOPHAN