Adenine nucleotide transport in sonic submitochondrial particles. Kinetic properties and binding of specific inhibitors

Abstract

1. 1. A procedure for preparation of sonic submitochondrial particles competent for adenine nucleotide transport is described. ADP or ATP transport was assayed, in the presence of oligomycin, in a saline medium made of 0.125 M KC1, 1 mM EDTA, 10 mM 4-morpholinopropane sulfonic acid buffer, pH 6.5. 2. 2. Sonic particles transport ADP and ATP by an exchange diffusion process. Externally added ADP (or ATP) is exchanged with internal ADP and ATP with a stoichiometry of one to one. The V value for ADP transport at 5 °C was between 2 and 3 nmol/min per mg protein. 3. 3. The transport system in sonic particles is specific for ADP and ATP. It is strongly dependent on temperature. The activation energy between 0 and 9 °C is approx. 35 kcal/mol. The optimum pH is 6.5. 4. 4. Like in intact mitochondria, externally added ADP is transported into sonic particles faster at a given concentration than externally added ATP. The V value for ADP transport is 1.5–2 times higher than the V value for ATP transport. 5. 5. The transition from the energized to the deenergized state in sonic particles results in a decrease of the pH gradient across the membrane (internal pH < external pH) and in a 2–4-fold increase in the K m value for ATP. This latter effect is opposite to that found for transport of added ATP in intact mitochondria (Souverijn, J. H. M., Huisman, L. A., Rosing, J. and Kemp, Jr., A. (1973) Biochim. Biophys. Acta 305, 185–198). Energization has no effect on the V value of ATP transport in sonic particles. 6. 6. In contrast to intact mitochondria, inhibition of ADP transport in sonic particles by bongkrekic acid does not have any lag-time and does not depend on pH. The inhibition caused by bongkrekic acid is a mixed type inhibition with a K i value of 1.2 μM. Atractyloside and carboxyatractyloside do not inhibit ADP transport in sonic particles, unless the particles have been preloaded with these inhibitors during the sonication. 7. 7. Palmityl-CoA added to sonic particles inhibits efficiently ADP transport. The mixed type inhibition found with palmityl-CoA has a K i of 1.6 μM. 8. 8. [ 3H]Bongkrekic acid binds to sonic particles readily and with high affinity. Bongkrekic acid binding to sonic particles does not depend on pH and it has a saturation plateau, corresponding approximately to 1.3 mol of site per mol of cytochrome a. The number of [ 3H]atractyloside binding sites is much lower (one-fifth of the bongkrekic acid). External carboxyatractyloside does not compete with [ 3H]bongkrekic acid for binding to sonic particles. However, when carboxyatractyloside is present inside the particles, it inhibits the binding of [ 3H]bongkrekic acid.