Photophysics and photochemistry of rose bengal bound to human serum albumin.
Rose bengal (RB) readily binds to human serum albumin (HSA). At low RB concentrations, 90% of the dye is associated to the protein (5 microM), This association takes place in specific binding sites I and/or II. At higher RB concentrations, unspecific binding takes place with up to 10 RB molecules bound per protein molecule. The behavior of excited RB molecules bound to HSA is widely different to that observed in aqueous solution. Furthermore, the data also show that the behavior of bound RB molecules changes with the average number of dye molecules per protein (n). In particular, when n is large, the fluorescence yield is significantly reduced and no measurable long-lived triples and free singlet oxygen formation from bound dyes is detected. These results are related to self-quenching of the singlet and, most likely, excited triplets. All results point to the relevance of intra-protein generated singlet oxygen. However, when the dye is bound to the protein, at low oxygen concentrations such as those prevailing in vivo, trapping by oxygen of the triplet becomes inefficient and type I processes could contribute to the observed photoprocesses.
Alarcón
Emilio
E
Facultad de Química, Departamento de Química Física, Pontificia Universidad Católica de Chile, Avda. Vicuña Mackenna 4860, Santiago, Chile.
Edwards
Ana Maria
AM
Aspée
Alexis
A
Borsarelli
Claudio D
CD
Lissi
Eduardo A
EA
D001665:Binding Sites; D055592:Biophysical Phenomena; D006801:Humans; D010777:Photochemistry; D017319:Photosensitizing Agents / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D012395:Rose Bengal / Q000737:chemistry / Q000378:metabolism*; D012709:Serum Albumin / Q000737:chemistry / Q000378:metabolism*; D026082:Singlet Oxygen / Q000378:metabolism
D017319:Photosensitizing Agents; D012709:Serum Albumin; D026082:Singlet Oxygen; D012395:Rose Bengal