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 from fast-twitch and slow-twitch skeletal muscle skinned fibers were comparatively analyzed. Electrophoretic patterns of fiber protein composition were also compared. It was found that fibers with low affinity of mitochondria for ADP (i.e., heart and slow-twitch skeletal muscle soleus) contain a 27.5-kD protein that is absent from the fibers that exert high affinity for ADP (i.e., fast-twitch skeletal muscle gastrocnemius). Partial proteolysis, which increases the affinity of mitochondria of the heart and slow-twitch skeletal muscles for ADP, results in the disappearance of this protein. The results suggest that this protein may be an intracellular factor that controls the permeability of the outer mitochondrial membrane for ADP.