A monoclonal antibody against cytochrome c oxidase distinguishes cardiac and skeletal muscle mitochondria.
The mitochondrial enzyme cytochrome c oxidase (COX) in eukaryotes consists of at least seven subunits, three of which (I-III) are encoded by mitochondrial DNA (mitDNA) and the others (IV-VII) by the nuclear genome. There is increasing evidence that COX in mammals exists in multiple tissue-specific forms, presumably specified by nuclearly encoded subunits. We performed immunologic studies in human cardiac and skeletal muscle, using a monoclonal antibody raised against subunit IV of COX purified from human cardiac muscle. In immunotitration studies, the antibody bound with high affinity to mitochondria from cardiac muscle, but reacted only weakly with mitochondria from skeletal muscle. Similarly, immunocytochemical studies showed prominent mitochondrial staining in frozen sections of heart, but no staining in sections of mature skeletal muscle. Although this antibody did not stain mitochondria in mature skeletal muscle, it clearly stained mitochondria in myoblasts and immature myotubes of human muscle cultures, suggesting that mitochondria in immature muscle cells are different from those in mature muscle, and similar to heart mitochondria. Immunotitration data using either native or denatured COX protein from heart or skeletal muscle showed similar immunoreactivity. These studies indicate that the epitope for recognition by this antibody is exposed in mitochondria from heart and immature muscle cells, but masked in mitochondria from mature skeletal muscle.
D000911:Antibodies, Monoclonal / Q000276:immunology; D046508:Culture Techniques; D003576:Electron Transport Complex IV / Q000032:analysis* / Q000276:immunology; D004797:Enzyme-Linked Immunosorbent Assay; D000939:Epitopes / Q000276:immunology; D005455:Fluorescent Antibody Technique; D006651:Histocytochemistry; D006801:Humans; D008929:Mitochondria, Heart / Q000201:enzymology*; D008931:Mitochondria, Muscle / Q000201:enzymology*
D000911:Antibodies, Monoclonal; D000939:Epitopes; D003576:Electron Transport Complex IV