Intramitochondrial metabolism of phosphoenolpyruvate.

Phosphoenolpyruvate was formed by rabbit liver mitochondria during incubations in the presence of dinitrophenol with oc-ketoglutarate and with other Krebs cycle intermediates as substrates. These intermediates, as indicated by experiments with labeled compounds, served as precursors for the carbon skeleton of the synthesized phosphoenolpyruvate. The phosphate, in the absence of exogenous supply, was derived from multiple endogenous sources; 70 to 90% was contributed by adenosine triphosphate, adenosine diphosphate, and inorganic phosphate. When a-ketoglutarate was the substrate, the synthesis of phosphoenolpyruvate was stimulated with addition of exogenous phosphate and was inhibited by arsenite and by arsenosophenylbutyrate. A portion of the phosphate, presumably, was activated by the succinic thiokinase reaction. On the other hand, when malate was the substrate, exogenous phosphate was not utilized, and the reaction was relatively insensitive to the arsenicals. In this case, phosphate was provided from endogenous sources by different, and as yet unidentified, reactions. In the presence of citrate, or in the presence of citrate and dinitrophenol, phosphoenolpyruvate was displaced from the mitochondria with inorganic phosphate but with only small losses of other organic phosphate compounds.