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 Mg(2+) cannot be replaced by Mn(2+). Allosterically inhibited by L-aspartate and L-malate. PEPC activity is not affected by allosteric activators of E.coli PEPC such as glucose 6-phosphate, fructose 1,6-bisphosphate, and acetyl coenzyme A. Optimum pH is 8.0. Optimum temperature is 90 degrees Celsius. Is extremely thermostable. No loss of activity is observed after incubation for 2 hours at 80 degrees Celsius. The times required for 50% loss of activity are about 60 minutes at 90 degrees Celsius, 10 minutes at 95 degrees Celsius, and 1 minute at 100 degrees Celsius. Homotetramer. Belongs to the PEPCase type 2 family. Extended N-terminus.