Evidence for net uptake and efflux of mitochondrial coenzyme A

Coenzyme A transport was studied by determining [14C]CoA associated with isolated rat heart mitochondria. HPLC analysis of a mitochondrial extract obtained following incubation with [14C] CoA revealed an increase in [14C] CoA. In the presence of pyruvate or alpha-ketoglutarate, [14C]CoA associated with mitochondria was converted to acetyl- or succinyl-[14C]CoA, respectively, demonstrating the intramitochondrial localization of transported CoA. Net uptake of CoA was demonstrated by the findings that the increase in mitochondrial content of CoA following incubation with CoA was equal to the values of CoA uptake obtained from experiments using [14C]CoA. Sequestration of intramitochondrial CoA as metabolically inert derivatives with maleate stimulated CoA uptake, supporting the concept of unidirectional CoA uptake rather than exchange. Altering the membrane electrochemical gradient with valinomycin, nigericin, calcium, phosphate or a combination of phosphate and calcium caused efflux of endogenous CoA. The largest efflux was observed with valinomycin or a combination of Ca2+ and Pi. The Ca2+ and Pi-induced CoA efflux was effectively prevented by succinate or pyruvate. The results suggest that the uptake process, which is dependent on the membrane electrical gradient can be reversed by dissipating the electrical gradient. The relevance of CoA efflux induced by Ca2+ and Pi is discussed with respect to reperfusion injury following ischemic damage. Other factors regulating the maintenance of CoA within the mitochondrial matrix include the matrix pH and the acylation state of CoA.