Roles of the soluble cytochrome c2 and membrane-associated cytochrome cy of rhodobacter capsulatus in photosynthetic electron transfer

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Genetic evidence indicates that Rhodobacter capsulatus has two different pathways for reduction of the photooxidized reaction center (RC) [Jenney, F. E., & Daldal, F. (1993) EMBOJ. 12, 1283-1292]. One pathway is via the water soluble cytochrome (cyt) c2, and the other is via a novel, membrane-associated c-type cytochrome, cyt cy, now believed to be identical to the cyt cx of Jones et al. [Jones, M. R., et al. (1990) Biochim. Biophys. Acta 975, 59-66] and c354 of Zannoni et al. [Zannoni, D., et al. (1992) Arch. Microbiol. 157, 367-374]. Mutants lacking either cyt c2, cyt cy, or the bc1 complex, as well as various combinations, were utilized to probe the functional role of these cytochromes in electron transfer. Data obtained by monitoring flash induced electron transfer kinetics in the RC, cyt c pool, cyt b, and the carotenoid band shift indicate that there are two pathways for electron transfer from the bc1 complex to the RC in R. capsulatus, one via cyt c2 and the other through cyt cy. The two pathways show strikingly different kinetics for RC reduction and cyt c oxidation, and both are present in the wild-type strain MT-1131. After genetic inactivation of both cyt c2 and cyt cy there remains no flash oxidizible c-type cytochrome, and inactivation of cyt cy rather than cyt c2 has a more pronounced effect on the extent of the light-induced membrane potential under the conditions tested. Finally, heme-stained SDS-PAGE and flash spectroscopy experiments indicate that cyt cy is detectable in strains lacking the bc1 complex when grown on minimal growth medium but not on rich medium. These findings complement the earlier genetic data and further establish that cyt cy is the electron carrier permitting soluble cyt c2-independent photosynthetic growth in R. capsulatus. © 1994 American Chemical Society.

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This article was published in Biochemistry, Volume 33, Issue 9, Pages 2496-2502.

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Copyright © 1994 Scopus.

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