COMPARATIVE-STUDY OF RESPIRATION KINETICS AND PROTEIN-COMPOSITION OF SKINNED FIBERS FROM VARIOUS TYPES OF RAT MUSCLE

The respiration parameters of mitochondria from rat heart muscle and f rom fast-twitch and slow-twitch skeletal muscle skinned fibers were co mparatively analyzed. Electrophoretic patterns of fiber protein compos ition were also compared. It was found that fibers with low affinity o f mitochondria for ADP (i.e., heart and slow-twitch skeletal muscle so leus) contain a 27.5-kD protein that is absent from the fibers that ex ert high affinity for ADP (i.e., fast-twitch skeletal muscle gastrocne mius). Partial proteolysis, which increases the affinity of mitochondr ia of the heart and slow-twitch skeletal muscles for ADP, results in t he disappearance of this protein. The results suggest that this protei n may be an intracellular factor that controls the permeability of the outer mitochondrial membrane for ADP.