Enables the transfer of a solute or solutes from one side of a membrane to the other according to the reaction: CoQH2 + 2 ferricytochrome c = CoQ + 2 ferrocytochrome c + 2 H+.
synonyms:
cytochrome a,
GO:0045153,
electron transporter, transferring electrons within cytochrome c oxidase complex activity,
complex III (mitochondrial electron transport) activity,