title: Stereochemistry of the reaction of sheep liver threonine dehydratase. A nuclear magnetic resonance and optical rotatory dispersion study of its reaction pathway and products.
abstract: 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.
mesh_terms: D000409:Alanine / Q000494:pharmacology; D000818:Animals; D002087:Butyrates / Q000378:metabolism; D003545:Cysteine / Q000494:pharmacology; D006836:Hydro-Lyases / Q000378:metabolism*; D007651:Keto Acids / Q000378:metabolism; D008099:Liver / Q000201:enzymology*; D009682:Magnetic Resonance Spectroscopy; D009905:Optical Rotatory Dispersion; D011422:Propionates / Q000378:metabolism; D012694:Serine / Q000378:metabolism; D012756:Sheep; D013237:Stereoisomerism; D013912:Threonine / Q000378:metabolism; D013913:Threonine Dehydratase / Q000378:metabolism*
chemical_list: D002087:Butyrates; D007651:Keto Acids; D011422:Propionates; D013912:Threonine; D012694:Serine; D006836:Hydro-Lyases; D013913:Threonine Dehydratase; D003545:Cysteine; D000409:Alanine