Recent Studies on the Mitochondrial Phosphate Transport Protein (PTP) and on its Relationship to the ADP/ATP Translocase (AAC) and the Uncoupling Protein (UCP)

Abstract

The metabolite carriers of the inner mitochondrial membrane perform essential functions by making the transport of metabolites compatible with the chemiosmotic hypothesis and providing a link for metabolic pathways separated by the mitochondrial inner membrane. Active research programs are being carried out to characterize these transport proteins. Studies have been reported on ten of these (Table 1) and have recently been summarized (Kramer & Palmieri, 1988). Some time ago, we embarked on a research program to identify the protein responsible for the transport of inorganic phosphate and to determine the mechanism by which the protein is able to carry out this transport. This phosphate transport protein (PTP) has been identified, purified, and its activity reconstituted (Wohlrab, 1986) and the sequence of the protein has been determined (Kolbe & Wohlrab, 1985; Runswick et al., 1987; Aquila et al., 1987). Our partial protein sequence permitted us to identify homologies between the PTP and the ADP/ATP carrier. At the same time, similar homologies between the sequence of the uncoupling protein (UCP) and that of the ADP/ATP translocase were also identified (Aquila et al., 1985). Thus while there are homologies among these three transport proteins, it will be of interest to determine whether non-phosphate (neither inorganic like PTP or organic like UCP or AAC) carriers such as the dicarboxylate, oxoglutarate, or monocarboxylate carriers will have similar homologies.