Proton Pump Activity in Bacterial Cytochrome Oxidases

Abstract

Many aerobic bacteria contain cytochrome aa 3 as a terminal oxidase as in the mitochondrial respiratory chain. This enzyme, cytochrome oxidase, is the coupling site (Site 3) where an electrochemical proton gradient (ΔµH+) is formed upon oxidation. Since 1979 these bacterial cytochrome oxidases have been highly purified from various bacteria (3–12). These enzymes are characterized by their simple subunit structure and similarity of prosthetic groups which consist of two a-hemes and two Cu atoms. For example cytochrome oxidase from the thermophilic bacterium PS3 which is a Gram-positive spore-forming thermophilic Bacillus, contains one copy of these subunits and 2 a-hemes and Cu atoms and shows very similar; enzymic properties to the mitochondrial enzyme, including possessing H+ pump activity. In the following, several topics concerning with bacterial cytochrome oxidases will be described in connection to proton pumping activity.