The Subunit Composition of Mammalian Cytochrome c Oxidase

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Abstract
Cytochrome c oxidase from rat liver mitochondria was separated into 12 different protein subunits by application of a highly resolving sodium dodecylsulfate/gel electrophoretic system of different compositions. The 12 protein subunits represent integral components of mammalian type cytochrome c oxidase for the following reasons. All 12 subunits copurify through various purification procedures. The subunit composition of the isolated enzyme is identical to that of the immunoprecipitated one. All 12 subunits are present in the complex at one to one stoichiometric amounts. A similar composition of 12 subunits was also found for cytochrome c oxidase from rat kidney, pig heart, rabbit liver and stone-marten liver. The difference between these results and other published data on the subunit composition of mammalian-type cytochrome c oxidase, based on gel electrophoretic analysis, is due to the insufficient resolving power of previously used gel systems and the very similar MW of subunits VIa,b,c and VIIa,b,c.