Involved in gluconeogenesis. Catalyzes the conversion of oxaloacetate (OAA) to phosphoenolpyruvate (PEP) through direct phosphoryl transfer between the nucleoside triphosphate and OAA (By similarity). ATP + oxaloacetate = ADP + CO2 + phosphoenolpyruvate Binds 1 Mn(2+) ion per subunit. Inhibited by p-chloromercuribenzoate. Optimum pH is between 6.7 and 7.1. The enzyme is stable from pH 5.0 to 9.0. It completely losing activity at pH values lower than 4.5 and retaining some activity in the pH range 9-12. Carbohydrate biosynthesis; gluconeogenesis. Monomer. Belongs to the phosphoenolpyruvate carboxykinase (ATP) family.