Reduction reactions of bovine serum albumin and lysozyme by CO- .2 radical in polyvinyl alcohol solution: a pulse radiolysis study

Pulse radiolytic reduction of bovine serum albumin (BSA) and lysozyme by CO^⨪₂ radical in presence of polyvinyl alcohol (PVA) has been studied. At pH 6.8 in presence of 2% (w/v) PVA, reduction of BSA and lysozyme (both at 1×10⁻⁴ mol dm⁻³) give an additional transient peak at 390 nm along with the usual 420 nm peak. The bimolecular rate constants for the reaction of CO^⨪₂ radical at pH 6.8±0.2 with BSA are 2.7×10⁸ and 7.13×10⁸ dm³ mol⁻¹ s⁻¹ at 420 nm and 390 nm respectively. The same for lysozyme are 3.2×10⁸ and 5.6×10⁸ dm³ mol⁻¹ s⁻¹ at 420 nm and 390 nm, respectively. Dimethyl disulfide also gives 390 nm and 420 nm peaks in this system upon reduction with CO^⨪₂ radical. The 390 nm peak is ascribed to the sulfenium radical (RSS(H)R). Studies on the variation of pH suggests the protonation of RSSR^⨪ radical (420 nm) to form RSS(H)R radical (390 nm) in this viscous media. The decay of RSS(H)R radical occurs via formation of RS radical and RS(H)S(H)R, the final product being RSH in both cases.