Regulation of pyruvate metabolism via pyruvate carboxylase in rat brain mitochondria

摘要

p1. The fixation of COsub2/sub by pyruvate carboxylase in isolated rat brain mitochondria was investigated. 2. In the presence of pyruvate, ATP, inorganic phosphate and magnesium, rat brain mitochondria fixed Hsup14/supCOsub3/subsup-/sup into tricarboxylic acid-cycle intermediates at a rate of about 250nmol/30min per mg of protein. 3. Citrate and malate were the main radioactive products with citrate containing most of the radioactivity fixed. The observed rates of Hsup14/supCOsub3/subsup-/sup fixation and citrate formation correlated with the measured activities of pyruvate carboxylase and citrate synthase in the mitochondria. 4. The carboxylation of pyruvate by the mitochondria had an apparent iKsubm/sub/i for pyruvate of about 0.5mm. 5. Pyruvate carboxylation was inhibited by ADP and dinitrophenol. 6. Malate, succinate, fumarate and oxaloacetate inhibited the carboxylation of pyruvate whereas glutamate stimulated it. 7. The results suggest that the metabolism of pyruvate via pyruvate carboxylase in brain mitochondria is regulated, in part, by the intramitochondrial concentrations of pyruvate, oxaloacetate and the ATP:ADP ratio./p