The Free‐Radical Cleavage of the Disulfide Bond (Studied by Pulse Radiolysis)

Reaction of H atoms with glutathione leads rapidly to H + RSSR → RS · + RSH. The first observed product is RS, the spectrum of which is obtained. The spectrum of the RS̄SR radical was obtained by direct attack of e − aq on glutathione. The rate constants of these processes were also measured. k e− aq + RSSR = (2.7 ± 0.3) × 10 9 M −1 sec −1 k H + RSSR = (1.0 ± 0.2) × 10 10 M −1 sec −1 When the OD of RS̄SR is plotted vs pH a titration curve is obtained. This is due to the protonation of RS̄SR with a rate constant of 2.6 × 10 10 M −1 sec −1 which is probably followed by a cleavage to RS and RSH. In both cases the RSSHR radical cannot be detected. The spectrum attributed to the RSSHR radical is more likely to be that of RS.