Involved in the gluconeogenesis. 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. Optimum pH is 7. Optimum temperature is 80 degrees Celsius. Thermostable. Half-life at the optimal temperature is 53 minutes. Carbohydrate biosynthesis; gluconeogenesis. Homotetramer. Belongs to the phosphoenolpyruvate carboxykinase [GTP] family.