Effect of Phosphoenolpyruvate and Oxaloacetate on Ca2+ Uptake by Isolated Mung Bean Mitochondria

Phosphoenolpyruvate partially inhibits the accumulation of Ca(2+) in isolated mung bean (Phaseolus aureus Roxb.) mitochondria. Succinate-supported Ca(2+) uptake is twice as sensitive to phosphoenolpyruvate inhibition as is NADH- or malate/pyruvate-supported Ca(2+) uptake. Pyruvate, atractylate, and ATP, but not ITP, reverse the phosphoenolpyruvate-induced inhibition. Oxaloacetic acid inhibits succinate-supported Ca(2+) uptake completely while partially inhibiting NADH-supported Ca(2+) uptake. The oxaloacetate inhibition of NADH-supported Ca(2+) uptake is greater than that produced by phosphoenolpyruvate. It is suggested that inhibition of Ca(2+) uptake is due to the conversion of phosphoenolpyruvate into oxaloacetate via phosphoenolpyruvate carboxykinase, with oxaloacetate responsible for the actual inhibition of Ca(2+) uptake.