Through the carboxylation of phosphoenolpyruvate (PEP) it forms oxaloacetate, a four-carbon dicarboxylic acid source for the tricarboxylic acid cycle. May be involved in phloem loading with sucrose and in anions and cations uptake and amino acid biosynthesis in roots. oxaloacetate + phosphate = hydrogencarbonate + phosphoenolpyruvate Activated by the allosteric regulator glucose-6-phosphate (By similarity). Inhibited by malate and aspartate (By similarity). Up regulated by light-reversible phosphorylation (By similarity). Homotetramer. Expressed in roots and stems and at low levels in leaves. Preferentially expressed in the phloem and in root tips. Belongs to the PEPCase type 1 family.