Paths of Carbon in Gluconeogenesis and Lipogenesis: VII. THE SYNTHESIS OF PRECURSORS FOR GLUCONEOGENESIS FROM PYRUVATE AND BICARBONATE BY RAT KIDNEY MITOCHONDRIA

Abstract

Abstract In the presence of ATP, Pi, and magnesium ions, rat kidney mitochondria converted pyruvate and bicarbonate mainly to malate, fumarate, and citrate. Pyruvate carboxylase activity was estimated by measuring the amounts of products formed and the radioactive bicarbonate retained. When glutamate was added to the system, radioactive aspartate was formed without changing the incorporation of radioactivity into malate and citrate. High concentrations of pyruvate, magnesium ions, or bicarbonate inhibited pyruvate carboxylation, as did the absence of added Pi. Addition of short chain fatty acids or of acylcarnitines of various chain lengths decreased pyruvate decarboxylation. In the presence of octanoate and hexanoate, the formation of malate and citrate and the incorporation of radioactive bicarbonate were slightly decreased. The addition of ammonium chloride led to formation of small amounts of aspartate, but otherwise did not alter product formation or bicarbonate incorporation. With liver mitochondria, addition of ammonium chloride permitted formation of aspartate and glutamate in large quantities and malate production was depressed. With kidney mitochondria, the addition of malate, succinate, α-ketoglutarate, or citrate led to large increases in bicarbonate incorporation into malate. Similar but smaller effects were observed with liver mitochondria. It is concluded that kidney pyruvate carboxylase is sufficiently active to permit this organ to contribute significantly to gluconeogenesis in the rat.