Stereochemistry and function of oxaloacetate keto-enol tautomerase.
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.[1]References
- Stereochemistry and function of oxaloacetate keto-enol tautomerase. Johnson, J.D., Creighton, D.J., Lambert, M.R. J. Biol. Chem. (1986) [Pubmed]
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