The two smallest polypeptide components of D. discoideum cytochrome c oxidase, whose alternative expression depends on oxygen concentration [Schiavo G. and Bisson R. (1989) J. Biol. Chem. 264, 7129-7134], have been partially sequenced. They show 45$ homology and are isoforms of the same subunit, which must be encoded on two different genes.
