Pyruvate metabolism in rat brain mitochondria.
1. Oxidation of pyruvate by rat brain mitochondria was stimulated in state 3 by malate or succinate up to 250 nmoles O2/mg protein/min. Oxidation of malate, succinate, 2-oxoglutarate or glutamate as the sole substrates, was 1/4 - 1/5 that observed with pyruvate. 2. Maximum oxygen consumption in state 3 was observed at pH 6.90 - 7.20, whereas in state 4 it was not affected by changes in pH. 3. In state 4, in the absence of exogenous acceptor or acetyl residues, acetate was the main oxidation product, corresponding to about 80% of the amount of pyruvate utilized. Malate did not affect the rate of pyruvate utilization but lowered acetate concentration and raised concentration of citrate and 2-oxoglutarate. 4. In state 3, pyruvate and malate were converted mainly to 2-oxoglutarate, its concentration being three times as high as that of citrate. 5. Formation of citrate, 2-oxoglutarate and acetate from pyruvate in brain is considered as a function of availability of the acceptor of acetyl residues and the energy state of mitochondrion.
Pyruvate metabolism in rat brain mitochondria. 1. Oxidation of pyruvate by rat brain mitochondria was stimulated in state 3 by malate or succinate up to 250 nmoles O2/mg protein/min. Oxidation of malate, succinate, 2-oxoglutarate or glutamate as the sole substrates, was 1/4 - 1/5 that observed with pyruvate. 2. Maximum oxygen consumption in state 3 was observed at pH 6.90 - 7.20, whereas in state 4 it was not affected by changes in pH. 3. In state 4, in the absence of exogenous acceptor or acetyl residues, acetate was the main oxidation product, corresponding to about 80% of the amount of pyruvate utilized. Malate did not affect the rate of pyruvate utilization but lowered acetate concentration and raised concentration of citrate and 2-oxoglutarate. 4. In state 3, pyruvate and malate were converted mainly to 2-oxoglutarate, its concentration being three times as high as that of citrate. 5. Formation of citrate, 2-oxoglutarate and acetate from pyruvate in brain is considered as a function of availability of the acceptor of acetyl residues and the energy state of mitochondrion.