CONTROL OF OXIDATIVE-PHOSPHORYLATION IN RAT-LIVER MITOCHONDRIA - EFFECT OF IONIC MEDIA

The aim of this work was to compare oxidative phosphorylation activity and its kinetic control on isolated rat liver mitochondria in either various ionic or sucrose isoosmotic media. Whatever the ionic medium, state 3 and uncoupled state respiratory rates were higher in ionic tha n in sucrose media, although state 4 respiration rate remained constan t. Moreover, under isoosmotic conditions, the salt concentration neces sary for half state 3 stimulation depends on the cation involved: for inorganic cations, these K-0.5 values increased, as did the absolute v alue of hydratation enthalpy. The ATP/O ratio did not vary in any medi um and matrix volume was about 20% increased in ionic media. JO(2) ver sus Delta p relationships were left-shifted in ionic media compared to sucrose medium: for the same respiratory rate, the protonmotive force maintained was lesser in ionic media. However, the relationship betwe en JO(2) and Delta p is unique whatever the ionic medium under study. In ionic media compared to the sucrose medium, kinetic control was inc reased on one of the protonmotive force generating systems (cytochrome c oxidase) and decreased on one of the protonmotive force dissipating systems (adenine nucleotide translocator), even if the fluxes increas ed. (C) 1997 Elsevier Science B.V.