Biosynthesis of dicarboxylic acids by carbon dioxide fixation. III. Enzymatic synthesis of iota-malic acid by reductive carboxylation of pyruvic acid.

A complete chemical balance which demonstrates the occurrence of Reaction 3 has now been obtained. There is no reaction in the absence of either TPN, .Zwischenferment, or “malic” enzyme. The rate of reaction is proportional to the concentration of “malic” enzyme and to the CO* tension. It is also possible to couple the isocitric dehydrogenase-oxalosuccinic carboxylase system (2) with “malic” enzyme and to obtain a reversible TPN-linked dismutation between d-isocitrate and pyruvate, or between