Through the carboxylation of phosphoenolpyruvate (PEP) it forms oxaloacetate, a four-carbon dicarboxylic acid source for the tricarboxylic acid cycle. oxaloacetate + phosphate = hydrogencarbonate + phosphoenolpyruvate Activated by glutamine and dihydroxyacetone phosphate. Inhibited by glutamate, aspartate, 2-oxoglutarate and malate. Optimum pH is 8.1. Exists as a homotetramer or heterooligomer. Belongs to the PEPCase type 1 family.