IMPORT OF STEROLS INTO MITOCHONDRIA OF THE YEAST SACCHAROMYCES-CEREVISIAE

An in vitro assay was designed to study the import of radiolabeled erg osterol and cholesterol from unilamellar vesicles into isolated mitoch ondria of the yeast Saccharomyces cerevisiae. Supply of ergosterol to the mitochondrial surface was enhanced by a cytosolic fraction contain ing a lipid transfer protein, whereas no such additive to the assay wa s required for cholesterol transport, Both sterols reached the inner m itochondrial membrane, During import, they were detected in contact si tes between the outer and the inner mitochondrial membrane supporting the idea, that these zones are sites of intramitochondrial lipid trans location, Transport of ergosterol between the outer and the inner mito chondrial membrane was not affected by addition of ATP, depletion of A TP caused by treatment of mitochondria with apyrase and oligomycin, an d incubation with the uncoupler CCCP, indicating that this process is energy-independent.