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Singlet Oxygen‐mediated Photobleaching of the Prosthetic Group in Hemoglobins and C‐Phycocyanin
Author(s) -
Tapia Guillermina,
Galetovic Alexandra,
Lemp Else,
Pino Eduardo,
Lissi Eduardo
Publication year - 1999
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1111/j.1751-1097.1999.tb08244.x
Subject(s) - singlet oxygen , photobleaching , chromophore , chemistry , photochemistry , phycocyanin , quantum yield , heme , singlet state , hemoglobin , oxygen , reaction rate constant , irradiation , kinetics , organic chemistry , fluorescence , enzyme , biology , cyanobacteria , physics , quantum mechanics , bacteria , nuclear physics , excited state , genetics
Proteins bearing colored prosthetic groups, such as the heme group in hemoglobin or the bilin group in c‐phy‐cocyanin, 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 times 10 9 and 4.2 times 10 8 M ‐l s ‐1 for hemoglobin and phycocyanin, respectively, the bleaching of the chromophore takes place with rate constants of 3.2 times 10 6 and ˜1 times 10 7 M ‐1 s ‐1 . Irradiation of phycocyanin with red light bleaches the chromophore with low yields (˜0.8 times 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 (˜10 ‐3 ) of free singlet oxygen production after irradiation of the protein.