title: Singlet oxygen-mediated photobleaching of the prosthetic group in hemoglobins and c-phycocyanin.
abstract: Proteins bearing colored prosthetic groups, such as the heme group in hemoglobin or the bilin group in c-phycocyanin, quench singlet oxygen by interactions at the apoprotein and the prosthetic group levels. In both proteins, chemical modification of the chromophore constitutes only a minor reaction pathway. While total deactivation of singlet oxygen takes place with rate constants of 4.0 x 10(9) and 4.2 x 10(8) M-1 s-1 for hemoglobin and phycocyanin, respectively, the bleaching of the chromophore takes place with rate constants of 3.2 x 10(6) and approximately 1 x 10(7) M-1 s-1. Irradiation of phycocyanin with red light bleaches the chromophore with low yields (approximately 0.8 x 10(-4)). Part of this bleaching is mediated by singlet oxygen produced by the irradiation of the bilin group. The low relevance of the singlet oxygen pathway is compatible with a low quantum yield (approximately 10(-3)) of free singlet oxygen production after irradiation of the protein.
authors.affiliation: Instituto de Química, Universidad Católica de Valparaiso, Santiago, Chile.
authors.forename: G
authors.initials: G
authors.lastname: Tapia
authors.forename: A
authors.initials: A
authors.lastname: Galetovic
authors.forename: E
authors.initials: E
authors.lastname: Lemp
authors.forename: E
authors.initials: E
authors.lastname: Pino
authors.forename: E
authors.initials: E
authors.lastname: Lissi
mesh_terms: D000458:Cyanobacteria / Q000737:chemistry / Q000528:radiation effects; D006454:Hemoglobins / Q000737:chemistry / Q000528:radiation effects*; D006801:Humans; D066298:In Vitro Techniques; D008706:Methemoglobin / Q000737:chemistry / Q000528:radiation effects; D010100:Oxygen / Q000737:chemistry / Q000528:radiation effects; D010777:Photochemistry; D010798:Phycocyanin / Q000737:chemistry / Q000528:radiation effects*; D026082:Singlet Oxygen
chemical_list: D006454:Hemoglobins; D010798:Phycocyanin; D026082:Singlet Oxygen; D008706:Methemoglobin; D010100:Oxygen