Pulse radiolysis of the eosin-human serum albumin complex

Abstract

The radiolysis of the eosin-human serum albumin (HSA) complex has been investigated with pulse radiolysis and ⁶⁰Co irradiation. The rate constant for the reaction of e^–_aq with eosin decreases from (1.94 ± 0.12)× 10¹⁰ 1/mol s in aqueous solution to (9 ± 1)× 10⁹ 1/mol s when the dye is fully bound to HSA at pH12. The reaction leads to the eosin semiquinone which is less strongly complexed to the protein than the dye. The G value for reductive bleaching of the complexed dye by ⁶⁰Co in the presence of D-glucose is 0.28, which is consistent with the effective encounter cross-section of the dye moiety. The reaction of hydroxyl radicals with HSA leads to a decrease in the ability to bind eosin, associated with the loss of solubility and not a specific attack on the binding sites.