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. Facilitates the recycling of lactate carbon in the liver. GTP + oxaloacetate = CO2 + GDP + phosphoenolpyruvate Binds 1 Mn(2+) ion per subunit. Carbohydrate biosynthesis; gluconeogenesis. Monomer. Present in liver and kidney. Appears to be constitutively expressed. In eukaryotes there are two isozymes: a cytoplasmic one and a mitochondrial one. In birds, PEPCK-M is the sole form of hepatic PEPCK, but it constitutes 60% of the enzyme in the kidney. Belongs to the phosphoenolpyruvate carboxykinase [GTP] family.