Partial deficiency of subunits in complex I or IV of patients with mitochondrial myopathies.

Subunits of Complexes I, III, IV, and V from skeletal muscle mitochondria isolated from four patients with mitochondrial myopathies were analyzed by immunoblotting. A deficiency was observed in Complex I or IV, or in both. The patterns of deficiency of subunits of each complex were similar both in patients with deficiency of a single complex and in patients with combined deficiency of the two complexes. The deficiency of any of these subunits was only partial, and no abnormalities in the electrophoretic mobilities of the subunits were observed. These results suggest that the deficiency of Complex I or IV in these patients are based on similar molecular defects which lead to decreased levels of these subunits.