Control of phosphoenolpyruvate synthesis in guinea-pig mitochondria.

1. The synthesis of phosphoenolpyruvate and the O(2) consumption from the tricarboxylic acid-cycle intermediates citrate, alpha-oxoglutarate, malate and succinate by guinea-pig mitochondria were compared. Malate was the most effective of these precursors; there was no synthesis of phosphoenolpyruvate from succinate. 2. The addition of palmitate, acetoacetate and ATP enhanced the synthesis of phosphoenolpyruvate from citrate and alpha-oxoglutarate. Palmitate and ATP increased the O(2) consumption, whereas acetoacetate had no effect on this parameter. 3. Octanoate depressed the synthesis of phosphoenolpyruvate from citrate, alpha-oxoglutarate and malate and increased the O(2) consumption. Pentenoic acid had no effect on phosphoenolpyruvate synthesis from any of the substrates used, although it increased the uptake of O(2). These findings might be relevant to the control of gluconeogenesis in vivo.