Energy-linked quinacrine fluorescence changes in submitochondrial particles from skeletal muscle mitochondria. Evidence for intramembrane H+ transfer as a primary reaction of energy coupling.

Submitochondrial particles obtained from skeletal muscle are open membrane fragments which show energy coupling yet cannot sustain transmembrane ion gradients. An energy-linked decrease in fluorescence emission of the fluorescent probe quinacrine is observed with skeletal muscle particles which is enhanced by the anion SCN-. This is essentially the same reaction observed with beef heart submitochondrial particles, in which the reaction is known to be a monitor of intramembrane H+ transfer. The results with skeletal muscle particles show that this intramembrane H+ transfer occurs in the absence of any electrochemical potential across the membrane. Further, it occurs independently of the direction of H+ exchange with the suspendingly medium, since energization of skeletal muscle submitochondrial particles is known to give H+ efflux into the medium, while energization of beef heart particles gives H+ uptake from the medium. We conclude that a primary reaction of energy coupling is intramembrane H+ transfer linked to electron transport but shielded from the suspending medium. Movements of H+ between membrane and medium are secondary reactions derived from the primary one, possibly linked by a series of intramembrane conformational changes comprising a sequential membrane Bohr effect.