Force-flow and back-pressure relationships in mitochondrial energy transduction: an examination of extended state 3-state 4 transitions.

Liver mitochondria were incubated through extended State 3-State 4 transitions (B. Chance and G. N. Williams (1955) J. Biol. Chem. 217, 409-423) in the presence of high concentrations of adenine nucleotides and in presence and absence of a protonophore. In the terminal phase of these transitions (the region of respiratory control), (a) there was a proportional relationship between the phosphorylation potential and membrane potential (delta psi); and (b) the rate of phosphorylation (Jp) was proportionately and inversely related to the back-pressure of delta psi (reflective of proton-motive force (delta p); (c) when phosphorylation was limited by the magnitude of delta psi in the presence of increasing [protonophore], Jp was proportionately and directly related to delta psi. The slopes of these two dependencies (a and c) were approximately equal, but opposite in sign. Protonophore or ADP, added separately, decreased delta psi but the extent of decrease in delta psi by ADP added after increasing amounts of protonophore decreased in a manner proportional to Jp. These data are in all respects consistent with bulk-phase delta p being the central intermediate driving (or suppressing) the phosphorylation reaction.