Mitochondrial phosphate transport and the N-ethylmaleimide binding proteins of the inner membrane.

Mitochondria have been prepared from the flight muscles of mature blow-flies (Sarcophaga bullata). Phosphate transport by these mitochondria, determined by rates of passive swelling in ammonium phosphate, is sensitive to inhibition by N-ethylmaleimide. 20 nmol of N-ethylmaleimide/nmol cytochrome A inhibit the swelling by 90%. When the mitochondria are inhibited by N-[3H]ethylmaleimide, then solubilized in dodecyl sulfate/mercaptoethanol at 100 degrees C and then electrophoresed on dodecyl sulfate-polyacrylamide gels, many labeled protein bands can be detected, including a large labeled peak that has the same mobility as the tracking dye, bromophenol blue. Sonic submitochondrial particles that are prepared from the N-[3H]ethylmaleimide-labeled mitochondria, solubilized, and electrophoresed on dodecyl sulfate-polyacrylamide gels, possess only seven major labeled protein bands with no radioactive peak at the tracking dye. These labeled proteins have molecular weights of 71, 68, 64, 45, 32, 30, and approx. 10 . 10(3). The nmol N-[3H]ethylmaleimide bound to each of these proteins per nmol cytochrome A are 0.15, 0.19, 0.35, 0.45, 0.87, 0.10, and 0.17, respectively, when the mitochondria are inhibited with 21.5 mol N-[3H]ethylmaleimide/mol cytochrome a at 10 micron cytochrome A. Coty and Pedersen (1975) J. Biol. Chem. 250, 3515-3521) sensitized rat liver mitochondria to N-[3H]ethylmaleimide and identified five labeled proteins. Only the labeled 32 . 10(3) dalton and the 45 . 10(3) dalton proteins are common to both systems.