Catalyzes the irreversible beta-carboxylation of phosphoenolpyruvate (PEP) to form oxaloacetate (OAA), a four-carbon dicarboxylic acid source for the tricarboxylic acid cycle. oxaloacetate + phosphate = hydrogencarbonate + phosphoenolpyruvate Inhibited by NaCl, KCl, ATP, ADP, GTP and aspartate. Unlike E.coli, not regulated by acetyl-CoA. Optimum pH is 6.8. Optimum temperature is 62 degrees Celsius. Homotetramer. Belongs to the PEPCase type 2 family. Extended N-terminus.