PCK2, the mitochondrial matrix form of phosphoenopyruvate carboxykinase, catalyzes the reaction of oxaloacetate and GTP to form phosphoenolpyruvate, GDP, and CO2. In the chicken, PCK2 is constitutively expressed in liver, where it is the only form of the enzyme, and kidney, where cytosolic PCK1 is also expressed (Kurahashi et al. 1957; Hod et al. 1982; Weldon et al. 1990).