Structural and functional aspects of the phosphate carrier from mitochondria

The paper reviews the major structural and functional aspects of the phosphate carrier from the inner mitochondrial membrane in comparison to other mitochondrial carrier proteins. The mitochondrial phosphate carrier catalyzes the transport of inorganic phosphate from the cytosol into the mitochondrial matrix and is thus essential for the energy metabolism of the cell. The phosphate carrier from beef and pig heart, from rat liver and from yeast mitochondria has been purified by chromatographic methods and functionally reconstituted in proteoliposomes. The primary sequence of the phosphate carrier from several different species has been determined. The carrier protein of Mr 33 to 34 kDa most likely acts as a dimer in the membrane. The phosphate carrier has been characterized with respect to transport kinetics, energy dependence and carrier mechanism mainly after functional reconstitution into artificial bilayers (liposomes). Three different modes of action were elucidated, namely homologous phosphate/phosphate antiport, heterologous phosphate/proton symport or phosphate/hydroxyl antiport, respectively, as well as unphysiological uniport (efflux) after modification of essential SH-groups. Both with respect to its primary structure and its functional (kinetic) properties, the phosphate carrier is a member of the well-defined mitochondrial carrier protein family.