Two routes for synthesis of phosphoenolpyruvate from C4-dicarboxylic acids in Escherichia coli

Mutants of $\text{E. coli}$ defective in both phosphoenolpyruvate carboxykinase and phosphoenolpyruvate synthetase are unable to use C₄-dicarboxylic acids such as succinate and malate as carbon and energy sources for growth. Revertants that have restored function for either one of these enzymes can grow in a malate-mineral medium, but at a reduced rate compared with the growth of wild-type cells. $\text{E. coli}$ appears to use two pathways for synthesis of phosphoenolpyruvate from C₄-dicarboxylic acids. One of these involves decarboxylation of oxalacetate catalyzed by phosphoenolpyruvate carboxykinase. The second pathway makes use of the combined action of malic enzyme and phosphoenolpyruvate synthetase.