NON-INHIBITING PERTURBATION OF THE PRIMARY ENERGY-CONVERSION SITE (Q(O) SITE) IN RHODOBACTER-CAPSULATUS UBIHYDROQUINONE-CYTOCHROME-C OXIDOREDUCTASE (CYTOCHROME BC(1) COMPLEX)

Ethanol added to Rhodobacter capsulatus chromatophore membranes contai ning the cytochrome bc(1) complex effectively uncouples the sensitivit y of the [2Fe-2S] cluster EPR spectrum to the number and redox state o f ubiquinone/ubihydroquinone within the Q(o) site. Ethanol has no effe ct upon the rate of catalysis, leading to a non-inhibiting perturbatio n of cytochrome bc(1) function. We suggest that displacement occurs by ethanol acting from the aqueous phase to successfully compete with th e Q(o) site ubiquinones and mater to hydrogen bond the NepsilonH atom( s) of the coordinating [2Fe-2S] cluster histidines, (C) 1998 Federatio n of European Biochemical Societies.