The oxidation of malic acid by Micrococcus lysodeikticus.

The reaction catalyzed by mammalian malic dehydrogenase (1) is characterized by its dependence upon DPN,l inhibition by traces of OAA, and stimulation by carbonyl-binding compounds such as cyanide (2, 3). It was of interest, therefore, when Krampitz (4), studying oxidation of malate by whole or acetone-treated cells of 1~~crococcus lysodeikticus, found accumulation of OAA during the reaction. OAA, furthermore, failed to inhibit, and cyanide or semicarbazide did not stimulate the reaction. McManus (5) confirmed these observations and, in addition, could find no dependence of malate oxidation upon DPN or TPN. The present investigation was initiated to study the manner in which malate is oxidized by M. lysodeikticus. Evidence has been obtained that at least two OAA-producing malic dehydrogenases are present in this microorganism, the first being DPN-dependent and the second not dependent upon this cofactor or TPN. Partial purification has permitted separation of these activities.