MEMBRANE-ASSOCIATED CYTOCHROME C(Y) OF RHODOBACTER-CAPSULATUS IS AN ELECTRON CARRIER FROM THE CYTOCHROME BC(1) COMPLEX TO THE CYTOCHROME-C-OXIDASE DURING RESPIRATION

We have recently established that the facultative phototrophic bacteri um Rhodobacter capsulatus has two different pathways for reduction of the photooxidized reaction center during photosynthesis (F, E, Jenney and F, Daldal, EMBO J, 12:1283-1292, 1993; F. E, Jenney, R. C, Prince, and F, Daldal, Biochemistry 33:2496-2502, 1993), One pathway is via t he well-characterized, water-soluble cytochrome c(2) (cyt c(2)), and t he other is via a novel membrane-associated c-type cytochrome named cy t c(y). In this work, we probed the role of cyt c(y) in respiratory el ectron transport by isolating a set of R. capsulatus mutants lacking e ither cyt c(2) or cyt c(y), in the presence or in the absence of a fun ctional quinol oxidase-dependent alternate respiratory pathway, The gr owth and inhibitor sensitivity patterns of these mutants, their respir atory rates in the presence of specific inhibitors, and the oxidation- reduction kinetics of c-type cytochromes monitored under appropriate c onditions demonstrated that cyt c(y), like cyt c(2), connects the bc(1 ) complex and the cyt c oxidase during respiratory electron transport, Whether cyt c(2) and cyt c(y) are the only electron carriers between these two energy-transducing membrane complexes of R. capsulatus is un known.