MS and MS/MS analysis of GSSG and its oxidation products. The experimental conditions were the same as described in the legend to Fig. 1. A, C, and E, mass spectrometric analysis (MS) of GSSG, peaks 1 and 2 (M-45) and peaks 3–5 (M-90), respectively; B, D, and F, tandem MS (MS/MS) analysis of m/z 613.1, 550.0, and 487.0, respectively.