Purification of the mitochondrial phosphate-hydroxyl ion antiporter from rat liver

Inorganic phosphate must be transported continuously into the mitochondrial matrix to maintain the steady-state oxidative phosphorylation of ADP. Specific uptake of this anion occurs via at least two distinct transport systems: an electroneutral inorganic phosphate-dicarboxylic acid exchange carrier and an inorganic phosphate-hydroxyl antiporter which catalyses the influx of about 90% of the mitochondrial phosphate. An interesting property of these phosphate transporters, which has facilitated their identification, is that they are inhibited by a low concentration of sulphydryl group reagents. The phosphate carrier protein is inhibited by N-ethylmaleimide, mersalyl and p-chloromercuribenzoic acid (Fonyo & Besman, 1968; Tyler, 1969; Coty & Pederson, 1974), whereas the phosphate-dicarboxylate exchange protein is blocked by mersalyl and p-chloromercuribenzoic acid but is insensitive to N-ethylmaleimide (Meyer & Tager, 1969; Meijer et al., 1970; Quagliariello & Palmieri, 1972; Coty & Pederson, 1974). In rat liver mitochondria, the phosphate carrier protein has been purified by modifying the method of Kolbe et al.