Aromatic 2-oxo acid reductase was purified to homogeneity from the cytosol of dog heart. The purified enzyme utilized various 2-oxo acids as substrates in the following order of activity: oxaloacetate > 3,5-diiodo-4-hydroxyphenylpyruvate > indolepyruvate > phenylpyruvate. Little or no activity was detected with glyoxylate, pyruvate, hydroxypyruvate, 2-oxoglutarate and 2-oxoadipate. NADH was active as coenzyme but not NADPH. The enzyme has an isoelectric point of 5.4 and is probably composed of two identical subunits with a molecular weight of approx. 40000. Evidence was presented that aromatic 2-oxo acid reductase is identical with one of the cytosol malate dehydrogenase isoenzymes. The enzyme was also found in the brain, kidney and liver of dog.
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