A new membrane-bound cytochrome c works as an electron donor to the photosynthetic reaction center complex in the purple bacterium, Rhodovulum sulfidophilum.
A new type of membrane-bound cytochrome c was found in a marine purple photosynthetic bacterium, Rhodovulum sulfidophilum. This cytochrome c was significantly accumulated in cells growing under anaerobic photosynthetic conditions and showed an apparent molecular mass of approximately 100 kDa when purified and analyzed by SDS-PAGE. The midpoint potential of this cytochrome c was 369 mV. Flash-induced kinetic measurements showed that this new cytochrome c can work as an electron donor to the photosynthetic reaction center. The gene coding for this cytochrome c was cloned and analyzed. The deduced molecular mass was nearly equal to 50 kDa. Its C-terminal heme-containing region showed the highest sequence identity to the water-soluble cytochrome c(2), although its predicted secondary structure resembles that of cytochrome c(y). Phylogenetic analyses suggested that this new cytochrome c has evolved from cytochrome c(2). We, thus, propose its designation as cytochrome c(2m). Mutants lacking this cytochrome or cytochrome c(2) showed the same growth rate as the wild type. However, a double mutant lacking both cytochrome c(2) and c(2m) showed no growth under photosynthetic conditions. It was concluded that either the membrane-bound cytochrome c(2m) or the water-soluble cytochrome c(2) work as a physiological electron carrier in the photosynthetic electron transfer pathway of Rvu. sulfidophilum.
Kimura
Yasuaki
Y
Department of Biological Science, Tokyo Metropolitan University, Minamiohsawa 1-1, Hachioji, Tokyo 192-0397, Japan.
Alric
Jean
J
Verméglio
André
A
Masuda
Shinji
S
Hagiwara
Yuuki
Y
Matsuura
Katsumi
K
Shimada
Keizo
K
Nagashima
Kenji V P
KV
D000693:Anaerobiosis; D001426:Bacterial Proteins / Q000502:physiology; D045304:Cytochromes c / Q000502:physiology*; D004579:Electron Transport / Q000502:physiology*; D007700:Kinetics; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009154:Mutation; D010084:Oxidation-Reduction; D045322:Photosynthetic Reaction Center Complex Proteins; D010802:Phylogeny; D041903:Rhodovulum / Q000737:chemistry*
D001426:Bacterial Proteins; D008565:Membrane Proteins; D045322:Photosynthetic Reaction Center Complex Proteins; D045304:Cytochromes c