spheroidene and bacteriopheophytin

A Rhodobacter capsulatus strain, designated XJ-1, isolated from saline soil, accumulated almost only one kind of bacteriochlorophyll a anaerobically in the light, aerobically in the light and dark, and the relative contents of the bacteriochlorophyll a were 44.61, 74.89, and 77.53% of the total pigments, respectively. A new purple pigment appeared only in aerobic-light grown cells, exhibited absorption maxima at 355, 389, 520, 621, and 755 nm, especially distinctly unusual peak at 621 nm, whereas vanished in anaerobic-light and in aerobic-dark culture. Spheroidene and OH-spheroidene predominated in anaerobic phototrophic cultures. Spheroidenone was the sole carotenoid when exposed to both light and oxygen. The second keto-carotenoids, OH-spheroidenone, presented only in aerobic-dark culture in addition to spheroidenone. Strain XJ-1 would be a good model organism for the further illustration of the regulation of bacteriochlorophyll biosynthesis gene expression in response to unique habitat.

Topics: Bacterial Proteins; Bacteriochlorophylls; Carotenoids; Light; Mass Spectrometry; Oxygen; Pheophytins; Rhodobacter capsulatus; Salinity; Sodium Chloride; Soil; Soil Microbiology

Photosynthetic reaction centres (RCs) catalyze light-driven electron, transport across photosynthetic membranes. The photosynthetic bacterium Rhodobacter, sphaeroides is often used for studies of RCs, and three groups have determined the structure of its reaction centre. There are discrepancies between these structures, however, and to resolve these we have determined the structure to higher resolution than before, using a new crystal form.. The new structure provides a more detailed description of the Rb. sphaeroides RC, and allows us to compare it with the structure of the RC from Rhodopseudomonas viridis. We find no evidence to support most of the published differences in cofactor binding between the RCs from Rps. viridis and Rb. sphaeroides. Generally, the mode of cofactor binding is conserved, particularly along the electron transfer pathway. Substantial differences are only found at ring V of one bacteriochlorophyll of the 'special pair' and for the secondary quinone, QB. A water chain with a length of about 23 A including 14 water molecules extends from the QB to the cytoplasmic side of the RC.. The cofactor arrangement and the mode of binding to the protein seem to be very similar among the non-sulphur bacterial photosynthetic RCs. The functional role of the displaced QB molecule, which might be present as quinol, rather than quinone, is not yet clear. The newly discovered water chain to the QB binding site suggests a pathway for the protonation of the secondary quinone QB.

Topics: Bacteriochlorophylls; Carotenoids; Electron Transport; Iron; Light-Harvesting Protein Complexes; Models, Molecular; Molecular Structure; Pheophytins; Photosynthetic Reaction Center Complex Proteins; Protein Conformation; Protons; Quinones; Rhodobacter sphaeroides