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Proton and cation movements associated with adp atp transport in mitochondria



Proton and cation movements associated with adp atp transport in mitochondria



European Journal of Biochemistry 82(2): 585-592



H+ and K+ movement associated with the [rat liver] mitochondrial ADP-ATP exchange were measured by glass electrode recordings in order to investigate the energy control of the ADP-ATP exchange. All measurements were taken in the presence of oligomycin and inhibitors of electron transport in order to exclude other types of H+ transfer. ATP exchange against endogenous ADP as induced by addition of ATP gives only a small H+ uptake which is partially suppressed in a KCl medium. H+ uptake is increased strongly on addition of uncoupler. On addition of valinomycin, K+ is taken up instead of H+. With carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP) and valinomycin, respectively, equivalent amounts of H+ and K+ are taken up over a wide range of protein and ATP concentration. The ATP dependence gives a ratio H+/ATP added = 0.38 and K+/ATP added = 0.27. Saturation with ATP is reached at about 14 .mu.mol ATP/g protein for H+ uptake and 20 .mu.mol ATP/g protein for K+ uptake. The FCCP-facilitated, ATP-induced H+ uptake increases with endogenous content of ADP, giving a ratio H+/ADP = 0.67. Kinetics of the H+ uptake and ATP-induced nucleotide exchange are closely correlated to about 0.62 H+/nucleotide released. The temperature dependence of the H+ uptake rate measured between 4 and 11.degree. C gives an activation energy = 33 kcal (138 kJ), similar to that found for the exchange rate. In the exchange of ADP against endogenous ATP as started by addition of ADP, H+ are released in the absence of FCCP. In the presence of FCCP, H+ release is only marked when endogenous nucleotides are preloaded with external ATP. This H+ release is decreased by Pi and enhanced by N-ethylmaleimide, blocking Pi transfer. It varies according to endogenous ATP content reaching the ratio H+ released/endogenous ATP = 0.3 to 0.5. These data indicate that the ATPe-ADPi exchange is largely electrical and the opposite ADPe-ATPi exchange is only between 50 to 70% electrical. The implications for energy transfer are discussed.

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