SUBUNIT-SPECIFIC MONOCLONAL-ANTIBODIES SHOW DIFFERENT STEADY-STATE LEVELS OF VARIOUS CYTOCHROME-C-OXIDASE SUBUNITS IN CHRONIC PROGRESSIVE EXTERNAL OPHTHALMOPLEGIA

Monoclonal antibodies recognizing the mitochondrially encoded subunits I and II, and the nuclear-encoded subunits IV, Va, Vb and VIc of huma n cytochrome-e oxidase were generated. These antibodies are highly spe cific and allow the assessment of subunit steady-state levels in crude cell extracts and tissue sections. In the experimental human cell lin e 143B206, which is devoid of mitochondrial DNA, immunovisualization w ith the antibodies revealed that the nuclear-encoded subunits IV and V a were present in amounts close to that of the parental cell line desp ite the absence of the mitochondrially encoded subunits. In contrast, the nuclear-encoded subunits Vb and VIc were severely reduced in cell line 143B206, suggesting that unassembled nuclear-encoded subunits are degraded at different rates. In skeletal muscle sections of a patient with chronic progressive external ophthalmoplegia known to harbor the 'common deletion' in a subpopulation of her mitochondrial DNA, most c ytochrome-e oxidase activity negative fibers had greatly reduced level s of subunits I, II, Va, Vb and Vie of cytochrome-c oxidase. The stead y-state level of subunit IV, however, was less affected. This was part icularly evident in cytochrome-c oxidase activity negative fibers with accumulated mitochondria ('ragged-red' fibers) where immunodetection with anti-subunit IV resulted in intense staining. The data presented in this paper demonstrate that the battery of monoclonal antibodies ca n be employed for diagnostic purposes to analyze steady-state levels o f mitochondrially and nuclear-encoded subunits of cytochrome-c oxidase .