Properties of protease-treated cytochrome c oxidase from beef heart.

About 45% of the protein can be removed from oxidized cytochrome c oxidase by treatment with proteolytic enzymes under a variety of conditions, leading to an increased heme to protein ratio. The principal spectroscopic parameters of cytochrome c oxidase are retained in the protease-treated enzyme. Of the overall catalytic activity 20% remained after digestion; the electron-transfer reactions were impaired but the affinity for cytochrome c appeared unchanged. Proteolysis resulted in removal of the hydrophobic subunit III and most of the smaller hydrophilic subunits, leaving a core, which basically consists of the two largest subunits I and II. The subunits I and/or II carry the prosthetic groups of the enzyme and at least one of the cytochrome c binding sites. The smaller subunits, however, are essential for optimal electron transfer and possibly have other functions as well.