Calcium uptake by reconstituted vesicles is mediated by a chymotrypsin-sensitive peptide associated with cytochrome oxidase

Abstract

Despite some controversy concerning the mechanism of Ca2+ uptake into mitochondria [ 1,2], it is generally agreed that the process is electrophoretic, driven by the respiratory activity of the inner mitochondrial membrane. A small polypeptide fulfilling the requirements of an ionophore has been isolated from calf heart mitochondria and it reportedly participates in the electrophoretic, ruthenium-red sensitive uptake of Ca2’ [3]. It was shown in [4,5] that submitochondrical particles prepared from beef heart and from rat liver mitochondria catalyze an energy-dependent inward movement of Ca’+. Because the sonic particles have an ‘inside-out’ polarity, their ability to accumulate Ca2+ was at variance with the electrophoretic uptake of Ca2+ into mitochondria. But these data became reconcilable in view of the evidence for more than one mitochondrial Ca2+ transport system [6]. Thus, the process in the inverted particles represented a mechanism for the efflux of Ca2+ through a Ca2’/H’ antiporter which is described in [7]. This efflux system is an electrically neutral, ruthenium-red insensitive process regulated by the oxidation-reduction state of pyridine nucleotides [8]. However, the complexity of Ca2+ movements is further illustrated by the finding that efflux mechanisms in different mammalian tissues are clearly dissimilar [9], a fact which undoubtedly contributes to some of the diverse interpretations of and controversies over the transport of Ca’+.