Roles of the Soluble Cytochrome c2 and Membrane-Associated Cytochrome cy of Rhodobacter capsulatus in Photosynthetic Electron Transfer

Abstract

Genetic evidence indicates that Rhodobacter capsulatus has two different pathways for reduction of the photooxidized reaction center (RC) [Jenney, F. E., & Daldal, F. (1993) EMBO J. 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 flas 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 cty 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.(ABSTRACT TRUNCATED AT 250 WORDS)

X-Ray Structure of Rhodobacter Capsulatus Cytochrome bc1: Comparison with its Mitochondrial and Chloroplast Counterparts

“…While the mitochondrial and bacterial enzymes are referred to as cyt bc 1 , the homologous enzyme in plant and algal chloroplasts and cyanobacteria is called plastohydroquinone : plastocyanin oxidoreductase or cyt b 6 f (for a review see Cramer et al 1996;Cramer et al 2004). In all cases, these energy transducing enzymes transfer electrons from a hydroquinone derivative (QH 2 ) (usually ubihydroquinone, menahydroquinone or plastohydroquinone), to an electron carrier molecue such as a c type cyt, a high potential iron sulfur protein (HiPIP) or a plastocyanin ( (Jenney and Daldal 1993;Jenney et al 1994;Hochkoeppler et al 1996;Kerfeld et al 1996) ). They are central players in respiration and photosynthesis as they contribute to the generation of an electrochemical potential ∆µH + , subsequently used for ATP production via the ATP synthase (Mitchell 1976;Dutton et al 1998;Saraste 1999).…”

“…These two proteins interact physically with very different electron acceptors: a c-type cyt (cyt c, c 2 , c y or c 8 ) (Jenney et al 1994;Kerfeld et al 1996) or a high potential iron-sulfur protein (HiPIP) (Hochkoeppler et al 1996) in the case of the cyt c 1 versus plastocyanin or a c-type cyt (cyt c 6 ) in the case of the cyt f (Cramer et al 1996). Moreover, the pH of the environment in which these subunits perform their specific functions is very different between the bacteria, mitochondria and chloroplasts.…”

Soluble Variants of Rhodobacter capsulatus Membrane-anchored Cytochrome cy Are Efficient Photosynthetic Electron Carriers

“…as described earlier (23). Chromatophore membranes used for SDS-PAGE/3,3Ј,5,5Ј-tetramethylbenzidine (TMBZ) or light-activated kinetic spectroscopy analyses were prepared in 50 mM MOPS buffer, pH 7.0, 1 mM phenylmethylsulfonyl fluoride dissolved in dimethyl sulfoxide and containing either 1 or 100 mM KCl, respectively (9). Protein concentrations were determined by the method of Lowry et al (24), and 16.5% SDS-PAGE analyses were performed as described by Schägger and von Jagow (25).…”

“…In the case of the widely studied anoxygenic, purple non-sulfur, facultative phototrophs of the genus Rhodobacter, Ps growth relies on cyclic electron transfer (ET) between the photochemical reaction center (RC) and the cyt bc 1 complex (3,4). In Rhodobacter capsulatus, either a soluble, freely diffusible cyt c 2 (5) or a membrane-anchored cyt c y (6, 7) reduces the photooxidized RC (8,9). On the other hand, in R. sphaeroides only the cyt c 2 fulfills this role, as the cyt c y homologue of this species is unable to support Ps growth (10).…”

Membrane‐Bound c ‐Type Cytochromes in Heliobacillus mobilis

“…The membrane-attached cytochrome c, (Jenney and Daldal, 1993) was shown to be involved in photosynthetic electron transport in Rhodobacter cupsulutus (Jenney et al, 1994). In most species of purple bacteria, a tetraheme cytochrome c, associated with the RC, is positioned between the diffusible carriers and the RC (reviewed by Nitschke and Dracheva, 1995).…”