title: Magnetic circular dichroism properties of reaction center complexes isolated from the zinc-bacteriochlorophyll a-containing purple bacterium Acidiphilium rubrum.
abstract: Reaction center (RC) complexes isolated from a Zn-bacteriochlorophyll (BChl) a-containing purple bacterium, Acidiphilium rubrum, were characterized by absorption, circular dichroism, and magnetic circular dichroism (MCD) spectroscopy. The oxidized-minus-reduced difference spectra indicated that, in this RC, the Zn-BChl a is the primary electron donor. The molecular structure of the donor was examined by measuring the ratio of the MCD intensity of the Faraday B-term (B) to the dipole strength (D). In the Q(y) region, B/D for the donor was about half those of bacteriopheophytin a and the accessory Zn-BChl a, indicating that the primary electron donor is a dimer. The magnitude of bleach of the Q(x) band was half that observed in Rhodobacter sphaeroides, suggesting the cation is localized on a single Zn-Bchl a. The absorption intensity of the higher-energy Q(y) exciton band was approximately 28% of that of the lower-energy band, and the exciton splitting was approximately 570 cm(-1), smaller than that in Rb. sphaeroides. These results indicate that, in A. rubrum, the primary electron donor is a Zn-BChl a dimer but that the interaction between the two molecules is rather weak. On the basis of these results, an adaptive strategy for changes in BChl a species is discussed from an evolutionary perspective.
authors.affiliation: Department of Physics, Faculty of Science, Yamaguchi University, Yamaguchi 753-8512, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Mimuro
authors.forename: M
authors.initials: M
authors.lastname: Kobayashi
authors.forename: K
authors.initials: K
authors.lastname: Shimada
authors.forename: K
authors.initials: K
authors.lastname: Uezono
authors.forename: T
authors.initials: T
authors.lastname: Nozawa
mesh_terms: D016947:Acetobacteraceae / Q000737:chemistry*; D001429:Bacteriochlorophylls / Q000737:chemistry*; D002942:Circular Dichroism; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins / Q000737:chemistry*; D015032:Zinc
chemical_list: D001429:Bacteriochlorophylls; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D015032:Zinc