Catalyzes the conversion of oxaloacetate (OAA) to phosphoenolpyruvate (PEP), the rate-limiting step in the metabolic pathway that produces glucose from lactate and other precursors derived from the citric acid cycle. GTP + oxaloacetate = CO2 + GDP + phosphoenolpyruvate Binds 1 Mn(2+) ion per subunit. Monomer. Belongs to the phosphoenolpyruvate carboxykinase [GTP] family.