Identification of the yeast mitochondrial transporter for oxaloacetate andsulfate

Saccharomyces cerevisiae encodes 35 members of the mitochondrial carrier fa mily, including the OAC protein. The transport specificities of some family members are known, but most are not, The function of the OAC has been reve aled by overproduction in Escherichia coli, reconstitution into liposomes, and demonstration that the proteoliposomes transport malonate, oxaloacetate , sulfate, and thiosulfate, Reconstituted OAC catalyzes both unidirectional transport and exchange of substrates, In S. cerevisiae, OAC is in inner mi tochondrial membranes, and deletion of its gene greatly reduces transport o f oxaloacetate sulfate, thiosulfate, and malonate. Mitochondria from wild-t ype cells swelled in isoosmotic solutions of ammonium salts of oxaloacetate , sulfate, thiosulfate, and malonate, indicating that these anions are cotr ansported with protons. Overexpression of OAC in the deletion strain increa sed greatly the [S-35]sulfate/sulfate and [S-35]sulfate/oxaloacetate exchan ges in proteoliposomes reconstituted with digitonin extracts of mitochondri a, The main physiological role of OAC appears to be to use the proton-motiv e force to take up into mitochondria oxaloacetate produced from pyruvate by cytoplasmic pyruvate carboxylase.