PNNL

Abstract

The cytochrome (cyt) bc1 complex is central to energy transduction in many species. Most investigators now accept a modified Q-cycle as the catalytic mechanism of this enzyme. Several thermodynamically favorable side reactions must be minimized for efficient functioning of the Q-cycle.Among these, reduction of oxygen by the Qo site semiquinone to produce superoxide is of special pathobiological interest. These superoxide-producing bypass reactions are most notably observed as the antimycin A- or myxothiazol-resistant reduction of cyt c. In this work, we demonstrate that these inhibitorresistant cyt c reductase activities are largely unaffected by removal of O2 in the isolated yeast cyt bc1 complex. Further, increasing O2 tension 5-fold stimulated the antimycin A-resistant reduction by a small amount (25%), while leaving the myxothiazol-resistant reduction unchanged.