Further studies on the effect of phosphoenolpyruvate on respiration-dependent calcium transport by rat heart mitochondria.

Phosphoenolpyruvate was found to depress extra oxygen consumption associated with Ca2+ -induced respiratory jump by rat heart mitochondria. Addition of phosphoenolpyruvate to mitochondria which have accumulated Ca2+ in the presence of glutamate and inorganic phosphate causes the release of Ca2+ from mitochondria. The phosphoenolpyruvate-stimulated Ca2+ efflux can be observed with mitochondria loaded with low initial Ca2+ concentration (0.12 mM) in the incubation medium. Measurements of mitochondrial H+ translocation produced by addition of Ca2+ to respiring mitochondria show that phosphoenolpyruvate depresses H+ ejection and enhances H+ uptake by mitochondria. The Ca2+ -releasing effect of phosphoenolpyruvate was found to be significantly stronger than that produced by rotenone when added to mitochondria loaded with Ca2+ in the presence of glutamate and inorganic phosphate. Dithiothreitol cannot overcome the effect of phosphoenolpyruvate on mitochondrial Ca2+ transport.