title: Cationic state distribution over the P700 chlorophyll pair in photosystem I.
abstract: The primary electron donor P700 in photosystem I is composed of two chlorophylls, P(A) and P(B). P700 forms the cationic [P(A)/P(B)](•+) state as a result of light-induced electron transfer. We obtained a P(A)(•+)/P(B)(•+) ratio of 28:72 and a spin distribution of 22:78 for the entire PSI protein-pigment complex. By considering the influence of the protein components on the redox potential for one-electron oxidation of P(A)/P(B) monomers, we found that the following three factors significantly contributed to a large P(B)(•+) population relative to P(A)(•+): 1), Thr-A743 forming a H-bond with P(A); 2), P(A) as a chlorophyll a epimer; and 3), a conserved PsaA/PsaB pair, the Arg-A750/Ser-B734 residue. In addition, 4), the methyl-ester groups of the accessory chlorophylls A(-1A)/A(-1B) significantly stabilized the cationic [P(A)/P(B)](•+) state and 5), the methyl-ester group orientations were completely different in A(-1A) and A(-1B) as seen in the crystal structure. When the methyl-ester group was rotated, the spin-density distribution over P(A)/P(B) ranged from 22:78 to 15:85.
authors: Career-Path Promotion Unit for Young Life Scientists, Graduate School of Medicine, Kyoto University, Kyoto, Japan.
authors: Keisuke
authors: K
authors: Saito
authors: Hiroshi
authors: H
authors: Ishikita
mesh_terms: D000595:Amino Acid Sequence; D002734:Chlorophyll / Q000737:chemistry* / Q000378:metabolism; D003067:Coenzymes / Q000378:metabolism; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000201:enzymology; D019281:Dimerization; D004579:Electron Transport; D006860:Hydrogen Bonding; D008958:Models, Molecular; D008968:Molecular Conformation; D008969:Molecular Sequence Data; D045331:Photosystem I Protein Complex / Q000737:chemistry* / Q000378:metabolism; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D011789:Quantum Theory; D013237:Stereoisomerism; D013816:Thermodynamics
chemical_list: D003067:Coenzymes; D045331:Photosystem I Protein Complex; D021122:Protein Subunits; D002734:Chlorophyll; C001785:chlorophyll P 700