Ubiquinone pair in the Qo site central to the primary energy conversion reactions of cytochrome bc1 complex.

摘要: The mechanistic heart of the ubihydroquinone-cytochrome c oxidoreductase (cyt bc1 complex) is catalytic oxidation ubihydroquinone (QH2) at Qo site. QH2 initiated by ferri-cyt c, mediated cyt c1 and [2Fe-2S] cluster cytochrome complex. in turn drives transmembrane electronic charge separation through two b-type hemes to another ubiquinone (Q) Qi In earlier studies, residues F144 G158 b-heme containing polypeptide Rhodobacter capsulatus complex were shown be influential site function. present study, have each been singly substituted neutral dissociation constants measured for both Q strong weak binding domains (Qos Qow). Various substitutions or found weaken affinities Qos Qow variably from zero beyond 10(3)-fold. This produced a family sites with domain occupancies ranging nearly full empty prevailing approximately 3 x 10(-2) M concentration membrane pool (Qpool). mutant, affinity remained typically 10-20-fold higher than that domain, as wild type, thereby indicating single mutations caused comparable extents weakening domain. Moreover, cause similar decreases maintaining Q/QH2 redox midpoint potentials (Em7) values type. Measurement yield rate generated turnover flashes mutants suggests serve different roles process. correlates linearly occupancy (QH2 Q), suggesting exchanges Qpool which much slower time scale turnover.(ABSTRACT TRUNCATED AT 400 WORDS)