Expression of the Escherichia coli cyo operon in Paracoccus denitrificans results in a fully active quinol oxidase of unexpected heme composition.

The cyo operon coding for the membrane-bound bo3-type quinol oxidase of Escherichia coli has been expressed in a Paracoccus denitrificans strain deleted in its endogenous ba3 quinol oxidase. Using the P. denitrificans qox promoter, the His tagged protein complex is synthesized to a level comparable to that in E. coli and the enzyme purified in a single step on a metal-chelating column. Whereas the activity of the isolated complex matches that of the oxidase purified directly from E. coli, the heterologously expressed oxidase does not show the characteristic heme composition but now carries heme a in its binuclear site.