Forms oxaloacetate through the carboxylation of phosphoenolpyruvate (PEP). Catalyzes the first step of C4 photosynthesis. oxaloacetate + phosphate = hydrogencarbonate + phosphoenolpyruvate 5 fold activation by the allosteric regulator glucose-6-phosphate (PubMed:24043710). Low sensitivity to inhibition by L-malate and L-aspartate (PubMed:23443546). Up-regulated by light-reversible phosphorylation (By similarity). Photosynthesis; C4 acid pathway. Homotetramer. Expressed in mesophyll cells, but not in bundle-sheath, roots, stems and flowers. Region 2 (296-437) and region 5 (645-966) are involved in the acquisition of C4-specific properties. Region 5 (645-966) is involved in L-malate tolerance. Ser-774 is strongly involved in determining allosteric behavior of C4 PEPC. Belongs to the PEPCase type 1 family.