The effect of oxalacetate on the oxidation of succinate by azotobacter extracts.

In the work by Stone and Wilson (1952) on the oxidative activity of Azotobacter extracts, the reactions of the citric acid cycle (Krebs, 1940) apparently offer the best mechanism for the results, but the slow oxidation of succinic acid remains unexplained. A clue to the solution is suggested by the work of Das (1937) and later, Pardee and Potter (1948), who found that oxalacetate in minute concentration was inhibitory to succinic acid dehydrogenase from animal tissue. Although Azotobacter extracts contain an active oxalacetate decarboxylase (Plaut and Lardy, 1949), it is possible that a sufficient residual concentration of oxalacetic acid exists in the presence of the decarboxylase to inhibit the succinic enzyme. If so, this would explain why acetic acid is rapidly oxidized when succinate is added to "spark" the reaction, but succinate itself is oxidized slowly because no acetate is present to remove the oxalacetate formed. If oxalacetate is the cause of the slow succinate reaction, it should be possible to show a temporary increase in the rate of succinate oxidation by adding glutamate which would in effect remove snall amounts of oxalacetate by the transamination equilibrium (Green et al., 1945) according to the relation: