title: Quantum yield of P700+ photodestruction in isolated photosystem I complexes of the cyanobacterium Arthrospira platensis.
abstract: The photostability of P700 cation radical (P700+) was studied by evaluating the quantum yields of P700(+) photodestruction in photosystem I (PSI) complexes of the cyanobacterium Arthrospira platensis. The time courses of P700+ photodestruction in PSI trimers and monomers have been measured in aerobic conditions under selective excitation of far-red absorption band of P700+ by intense light of laser diodes. Long-term exposure of PSI complexes to 808 or 870 nm laser light caused destruction of P700+ and antenna chlorophylls. The true integral quantum yield of P700+ photodestruction calculated from these data was less than 0.7-1.4 x 10(-8). Illumination of PSI complexes by 650 nm light caused destruction of antenna chlorophylls with true quantum yield of about 6-7 x 10(-6) and damage of P700 with apparent quantum yield 2-3 x 10(-8). Preferential photodestruction of the long-wavelength antenna chlorophyll absorbing at 710 nm as compared with bulk chlorophylls was observed. About three orders of difference in magnitude between quantum yields of P700+ and bulk chlorophyll photodestruction indicates that P700+ is extremely photostable for functioning as an efficient quencher of singlet excitation energy in PSI.
authors.affiliation: A.N. Bakh Institute of Biochemistry RAS, Leninsky pr. 33, 119071, Moscow, Russia.
authors.forename: Vladimir V
authors.initials: VV
authors.lastname: Shubin
authors.forename: Irina N
authors.initials: IN
authors.lastname: Terekhova
authors.forename: Boris A
authors.initials: BA
authors.lastname: Kirillov
authors.forename: Navassard V
authors.initials: NV
authors.lastname: Karapetyan
mesh_terms: D000458:Cyanobacteria / Q000378:metabolism / Q000528:radiation effects*; D045331:Photosystem I Protein Complex / Q000378:metabolism / Q000528:radiation effects*; D011789:Quantum Theory
chemical_list: D045331:Photosystem I Protein Complex