STRUCTURE AND EVOLUTION OF CYTOCHROME-OXIDASE

The structural features of cytochrome oxidases are reviewed in light of their evolution. The substrate specificity (quinol vs. cytochrome c) is reflected in the presence of a unique copper centre (Cu-A) in cytochrome c oxidases. In several lines of evolution, quinol oxidases have independently lost this copper. Also, the most primitive cytochrome c oxidases do not contain this copper, and electron entry takes place via c-type haems. These enzymes, exemplified by the rhizobial FixN complex, probably remind the first oxidases. They are related to the denitrification enzyme nitric oxide reductase.