Expression studies on the ba3 quinol oxidase from Paracoccus denitrificans. A bb3 variant is enzymatically inactive.

Expression of the quinol oxidase from Paracoccus denitrificans has been examined using a polyclonal antibody directed against subunit II and a promoter probe vector carrying the promoter region of the qox operon. Under aerobic conditions nitrate and nitrite act as specific inducers of the expression. To obtain an enzymatically competent quinol oxidase complex, an intact ctaB gene is required, which constitutes part of the cta operon coding for the aa3 cytochrome c oxidase of P. denitrificans. Deletion of ctaB leads to a change in heme composition of the quinol oxidase with heme b replacing the high-spin heme a of the binuclear center, causing loss of electron transport activity.