Johnson J D, Creighton D J, Lambert M R
J Biol Chem. 1986 Apr 5;261(10):4535-41.
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.
从猪肾中部分纯化得到的草酰乙酸酮 - 烯醇互变异构酶，通过一种机制催化烯醇式草酰乙酸向酮式草酰乙酸的转化，在该机制中，溶剂质子最终在酮式草酰乙酸C3的两个前手性位置上均匀分布。这一结论基于以下观察结果：当在过量苹果酸脱氢酶和NADH存在的情况下于3H2O中进行酶催化的酮化反应时，分离得到的(2S)-[3-3H]苹果酸中只有50%的3H在用延胡索酸酶处理后会释放到溶剂中。从立体化学角度来看，这种酶不同于已知催化溶剂与酮底物的前R位置之间立体特异性质子转移的苯丙酮酸酮 - 烯醇互变异构酶。作为试图阐明草酰乙酸互变异构酶活性生理重要性的结果，基于动力学和同位素捕获实验的结果，证明酮式草酰乙酸可直接穿过大鼠肝线粒体的内膜。
