Stereochemistry of the reaction of sheep liver threonine dehydratase. A nuclear magnetic resonance and optical rotatory dispersion study of its reaction pathway and products

• Published in: Biochemistry (Easton) Vol. 15; no. 17; pp. 3745 - 3749
• Main Authors: Kapke, Gordon, Davis, Leodis
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 24.08.1976
• Subjects: Alanine - pharmacology; Animals; Butyrates - metabolism; Cysteine - pharmacology; Hydro-Lyases - metabolism; Keto Acids - metabolism; Liver - enzymology; Magnetic Resonance Spectroscopy; Optical Rotatory Dispersion; Propionates - metabolism; Serine - metabolism; Sheep; Stereoisomerism; Threonine - metabolism; Threonine Dehydratase - metabolism
• ISSN: 0006-2960; 1520-4995
• DOI: 10.1021/bi00662a016

Products, substrates, and inhibitors of the threonine dehydratase from sheep liver (EC 4.2.1.16) have been investigated by proton nuclear magnetic resonance and optical rotation. The alpha-ketobutyrates produced from L-threonine and L-allothreonine in 2H2O have been shown to incorporate a single deuterium into the beta position. The dehydratase forms R-alpha-ketobutyrate-beta-d from L-threonine and L-allothreonine. The alpha protons of the substrates, threonine and allothreonine, do not exchange in the presence of the dehydratase. In the presence of dehydratase, the competitive inhibitors L-cysteine and L-alanine undergo alpha-proton exchange. Highly purified dehydratase has been used to determine kinetic parameters for the usbstrates L-threonine, L-allothreonine, L-serine, and L-chloroalanine. L-Chloroalanine, in addition to being a substrate, inhibits the dehydratase in a manner kinetically identical with that of L-serine.