A novel membrane-associated c-type cytochrome, cyt cy, can mediate the photosynthetic growth of Rhodobacter capsulatus and Rhodobacter sphaeroides.

Abstract

Mutants of Rhodobacter capsulatus lacking the soluble electron carrier cytochrome c2 are able to grow photosynthetically (Ps+), whereas Rhodobacter sphaeroides is unable to do so. To understand this unusual electron transfer pathway the gene required for cyt c2‐independent growth of R.capsulatus was sought using chromosomal libraries derived from a cyt c2‐ mutant of this species to complement a Ps‐ cyt c2‐ mutant of R.sphaeroides to Ps+ growth. The complementing 1.2 kbp DNA fragment contained a gene, cycY, encoding a novel membrane‐associated c‐type cytochrome, cyt cy, based on predicted amino acid sequence, optical difference spectra and SDS‐PAGE analysis of chromatophore membranes. The predicted primary sequence of cyt cy is unusual in having two distinct domains, a hydrophobic amino‐terminal region and a carboxyl‐terminus with strong homology to cytochromes c. A cyt cy‐ mutant of R.capsulatus remains Ps+ as does the cyt c2‐ mutant. However, a mutant lacking both cyt c2 and cy is Ps‐, and can be complemented to Ps+ by either cyt c2 or cyt cy. These findings demonstrate that each of the cytochromes c2 and cy is essential for photosynthesis only in the absence of the other. Thus, two distinct electron transfer pathways, unrecognized until now, operate during photosynthesis in R.capsulatus under appropriate conditions, one via the soluble cyt c2 and the other via the membrane‐associated cyt cy.

A High‐Potential Soluble Cytochrome C ‐551 from the Purple Phototrophic Bacterium Chromatium vinosum is Homologous to Cytochrome C8 from Denitrifying Pseudomonads

“…The gene product, cytochrome c,, has not been isolated. We also cannot exclude the possibility that a more strongly membrane bound cytochrome c,, comparable to cytochrome cy from R. capsulatus (Jenney et al, 1993) is the actual electron mediator.…”

“…5 ) but no one has demonstrated its role in photosynthesis. The only type of cytochrome that has been clearly demonstrated to be the electron-donor partner of the photoreaction cen-69.5 ter is the cytochrome c, from the non-sulfur bacteria Rhodobacter sphaeroides and Rhodobacter capsulatus (Donohue et al, 1988;Jenney and Daldal, 1993;Wang et al, 1994;Meyer and Donohue, 1995). C. vinosum, which in contrast with the latter bacteria has a tetrahaem cytochrome associated with its reaction center, may consequently have a cytochrome donor different from a c,-like protein.…”

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).…”

During Cytochrome c Maturation CcmI Chaperones the Class I Apocytochromes until the Formation of Their b-Type Cytochrome Intermediates

“…These include the class I C-terminally membrane-bound cytochrome c 1 subunit of the cytochrome bc 1 complex (8) and the N-terminally membrane-attached cytochrome c p and c o subunits of the cbb 3 -type oxygen reductase (9,10), as well as the soluble cytochrome c 2 and the N-terminally membrane-attached cytochrome c y as electron carriers (11,12). The class II soluble high-spin cytochrome cЈ is involved in NO detoxification (13), and the class III membrane-attached pentaheme c-type cytochrome DorC con-veys electrons from the Q/QH 2 pool to dimethyl sulfoxide (DMSO) 3 reducing it to dimethylsulfide (14).…”