STUDIES ON THE REDOX CENTERS OF THE TERMINAL OXIDASE FROM DESULFOVIBRIO-GIGAS AND EVIDENCE FOR ITS INTERACTION WITH RUBREDOXIN

Rubredoxin-oxygen oxidoreductase (ROO) is the final component of a sol uble electron transfer chain that couples NADH oxidation to oxygen con sumption in the anaerobic sulfate reducer Desulfovibrio gigas. It is a n 86-kDa homodimeric flavohemeprotein containing two FAD molecules, on e mesoheme IX, and one Fe-uroporphyrin I per monomer, capable of fully reducing oxygen to water. EPR studies on the native enzyme reveal two components with g values at similar to 2.46, 2.29, and 1.89, which ar e assigned to low spin hemes and are similar to the EPR features of P- 450 hemes, suggesting that ROO hemes have a cysteinyl axial ligation. At pH 7.6, the flavin redox transitions occur at 0 +/- 15 mV for the q uinone/semiquinone couple and at -130 +/- 15 mV for the semiquinone/hy droquinone couple; the hemes reduction potential is -350 +/- 15 mV. Sp ectroscopic studies provided unequivocal evidence that the flavins are the electron acceptor centers from rubredoxin, and that their reducti on proceed through an anionic semiquinone radical. The reaction with o xygen occurs in the flavin moiety. These data are strongly corroborate d by the finding that rubredoxin and ROO are located in the same polyc istronic unit of D. gigas genome. For the first time, a clear role for a rubredoxin in a sulfate-reducing bacterium is presented.