Through the carboxylation of phosphoenolpyruvate (PEP) it forms oxaloacetate, a four-carbon dicarboxylic acid source for the tricarboxylic acid cycle. Contributes probably to the adaptation to inorganic phosphate (Pi) deprivation. oxaloacetate + phosphate = hydrogencarbonate + phosphoenolpyruvate Magnesium. Can also use manganese. By light-reversible phosphorylation (By similarity). Activated by inorganic phosphate (Pi) deprivation and glucose 6-phosphate. Inhibited by L-malate and L-aspartate. Optimum pH is 8-9. Homotetramer. Expressed in all plant organs, with higher levels in roots. Upon inorganic phosphate (Pi) deprivation. The phosphorylation of Ser-11 is reversibly promoted by inorganic phosphate (Pi) deprivation. Enhanced activity by phosphorylation at pH 7.3 by lowering Km and sensitivity to inhibition by L-malate and L-aspartate, while enhancing activation by glucose 6-phosphate. Belongs to the PEPCase type 1 family.