title: Stereochemistry and function of oxaloacetate keto-enol tautomerase.
abstract: Oxaloacetate keto-enol tautomerase, partially purified from porcine kidney, catalyzes the conversion of enol- to keto-oxaloacetate by a mechanism in which solvent protons end up equally distributed between the two prochiral positions at C3 of keto-oxaloacetate. This conclusion is based upon the observation that when enzyme catalyzed ketonization is conducted in 3H2O in the presence of excess malate dehydrogenase and NADH, only 50% of the 3H in the isolated (2S)-[3-3H]malate is labilized to solvent upon treatment with fumarase. From a stereochemical perspective, this enzyme is unlike phenylpyruvate keto-enol tautomerase that is known to catalyze stereospecific proton transfer between solvent and the pro-R position of keto-substrate. As a result of an attempt to clarify the physiological importance of oxaloacetate tautomerase activity, keto-oxaloacetate was demonstrated to be directly transported across the inner membrane of rat liver mitochondria on the basis of the results of kinetic and isotope-trapping experiments.
mesh_terms: D000818:Animals; D005649:Fumarate Hydratase / Q000378:metabolism; D019746:Intramolecular Oxidoreductases; D007535:Isomerases / Q000302:isolation & purification / Q000378:metabolism*; D007668:Kidney / Q000201:enzymology*; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D013237:Stereoisomerism; D013379:Substrate Specificity; D013552:Swine; D014316:Tritium
chemical_list: D014316:Tritium; D005649:Fumarate Hydratase; D007535:Isomerases; D019746:Intramolecular Oxidoreductases; C048474:oxaloacetate tautomerase