title: Reaction center triplet states in photosystem I and photosystem II.
abstract: A photosystem I (PS I) particle has been prepared by lithium dodecyl sulfate digestion which lacks the acceptor X, and iron-sulfur centers B and A. Illumination of these particles at liquid helium temperature results in the appearance of a light-induced spin-polarized triplet signal observed by EPR. This signal is attributed to the triplet state of P-700, the primary donor, formed by recombination of the light induced radical pair P-700+ A1- (where A1 is the intermediate acceptor). Formation of the triplet does not occur if P-700 is oxidized or if A1 is reduced, prior to the illumination. A comparison of the P-700 triplet with that of P-680, the primary donor of Photosystem II, shows several differences. (1) The P-680 triplet is 1.5 mT (15 G) wider than the P-700 triplet. This is reflected by the zero-field splitting parameters, which indicate that P-700 is a slightly larger species than P-680. The zero-field splitting parameters do not indicate that either P-700 or P-680 are dimeric. (2) The P-700 triplet is induced by red and far-red light, while the P-680 triplet is induced only by red light. (3) The temperature dependences of the P-700 triplet and the P-680 triplet are different.
mesh_terms: D002736:Chloroplasts / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D004579:Electron Transport; D005615:Freezing; D007700:Kinetics; D008027:Light; D010084:Oxidation-Reduction; D010788:Photosynthesis; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D010940:Plant Proteins / Q000378:metabolism*; D010944:Plants
chemical_list: D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D010940:Plant Proteins