The subunit composition of pea cytochrome c oxidase

Cytochrome c oxidase was purified from pea shoots in a form containing more than 12 nmol of heme a per mg protein, but rapid inactivation took place during purification. On slab polyacrylamide concentration gradient gel electrophoresis of a partially purified preparation, there were three activity-bands corresponding to main protein bands. The activity-bands, as well as the most purified preparation, contained five polypeptides of different molecular weights (39,000, 33,000, 28,500, 16,500, and 8,000-6,000) as shown by sodium dodecylsulfate-urea polyacrylamide gel electrophoresis. However, an immunoprecipitate from the partially purified preparation with antibody against the most purified preparation contained two additional polypeptides with molecular weights of 13,000 and 10,000. Pea cytochrome c oxidase resembled the sweet potato enzyme with respect to immunological properties and absorption spectra as well as the subunit composition. We propose that higher plant cytochrome c oxidase is composed of five subunits of different molecular weights and is associated weakly with two low-molecular-weight polypeptides in the mitochondrial inner membrane.