Schematic representation of the respiratory chain of Aeropyrum pernix K1. Genes encoding cytochrome c oxidase and other respiratory components in the bacterium are indicated. ORFs APE_1719.1, APE_1724.1 and APE_1725 encode the cytochrome c553 complex which was isolated in this study. ORFs APE_0792.1, APE_0793.1 and APE_0795.1, annotated as aoxABC genes, encode an A-type cytochrome c oxidase, and ORFs APE_1623 and APE_1720 encode a B-type cytochrome c oxidase. In the previous study of Ishikawa et al. (2002), these 2 terminal oxidases were designated as cytochrome aa3- and ba3-type cytochrome c oxidase, respectively.