The Synthesis of Phosphoenolpyruvate in the Gluconeogenesis

Livers of chick embryos at different stages of incubation have been fractionated into mitochondrial and “soluble” fractions by centrifugation. The pyruvate carboxylase and phosphoenolpyruvate carboxykinase activities, which constitute the major pathway for the synthesis of phosphoenolpyruvate, have been measured in both preparations. The pyruvate carboxylase activity occurs only in the mitochondria and parallels the gluconeogenetic ability. The bulk of phosphoenolpyruvate carboxykinase activity appears in the mitochondria. Only traces can be detected in the “soluble” fraction. The level of the mitochondrial phosphoenolpyruvate carboxykinase activity varies during the incubation period in accordance with its presumed role as a major source of phosphoenolpyruvate in the gluconeogenesis. The hypothesis that the pathway of synthesis of phosphoenolpyruvate in the process of gluconeogenesis is mainly located in the mitochondria of chick embryo liver is proposed.