The terminal oxidases of Paracoccus denitrificans.

Three distinct types of terminal oxidases participate in the aerobic respiratory pathways of Paracoccus denitrificans. Two alternative genes encoding sub unit I of the aa3 -type cytochrome c oxidase have been isolated before, namely ctaDI and ctaDII. Each of these genes can be expressed separately to complement a double mutant (ActaDI, ActaDII), indicating that they are isoforms of subunit I of the aa3 -type oxidase. The genomic locus of a quinol oxidase has been isolated: cyoABC. Thisprotohaem-containing oxidase, called cytochrome bb3 , is the oniy quinoi oxidase expressed under the conditions used, in a triple oxidase mutant (ActaDI, ActaDII, cyoB::KmR ) an alternative cyto-chrome c oxidase has been characterized; this cbb3 -type oxidase has been partially purified. Both cytochrome aa3 and cytochrome bb3 are redox-driven proton pumps. The proton-pumping capacity of cytochrome cbb3 has been analysed; arguments for and against the active transport of protons by this novel oxidase complex are discussed.