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  • Title: Location of heme a on subunits I and II and copper on subunit II of cytochrome c oxidase.
    Author: Winter DB, Bruyninckx WJ, Foulke FG, Grinich NP, Mason HS.
    Journal: J Biol Chem; 1980 Dec 10; 255(23):11408-14. PubMed ID: 6254967.
    Abstract:
    A systemic study has been made of copper and heme a binding to subunits of beef heart cytochrome c oxidase. Copper and heme a were readily mobilized by ionic detergents, high ionic strengths, temperatures above 0 degrees C, thiol compounds, and gel-bound peroxides and free radicals when the subunits of the oxidase were dissociated from one another during polyacrylamide gel electrophoresis. Most subunits showed some affinity for heme a and copper under these conditions. However, in the presence of specific mixtures of ionic and nonionic detergents (e.g. 0.1% sodium dodecyl sulfate, 0.025% Triton X-100) at temperatures below 0 degrees C and in buffers of low ionic strength using 10 to 12% polyacrylamide gels preelectrophoresed for 3 days with thioglycolate, about 90% of the Cu was found on subunit II (Mr = 24,100), and heme a was found in equal amounts of subunits I (Mr = 35,800) and II. The oxidized-reduced and reduced-CO absorption spectra of these subunits resembled those of cytochrome c oxidase. It appears probable that in the native enzyme, subunit I contains heme a and subunit II contains copper and heme a. A relationship of mammalian cytochrome c oxidase to the two-subunit microbial cytochrome oxidase systems appears to exist.
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