Interrelationships of oxalacetic and l-malic acids in carbon dioxide fixation.

Reaction 1 requires TPN,’ as shown, while the incorporation of COZ into oxalacetate during Reaction 2 is catalyzed by ATP in pigeon liver extracts (4, 5), although not in bacterial preparations (6). The relationship between the two reactions has been obscure, although some information is available. It has been reported that ATP has no effect on Reaction 1 (1) and that TPN cannot replace ATP in Reaction 2 (5).2 Ochoa et al. (1) believe that it is unlikely that Reaction 1 is a summation of Reaction 2 and an oxidation-reduction reaction similar to that catalyzed by malic dehydrogenase, since oxalacetate cannot be substituted for pyruvate and COZ in reversing Reaction 1. Recently Veiga Salles et al. (7) suggested that Reaction 1 may be the primary reaction for CO2 fixation in dicarboxylic acids and that the reversal