Figure 2. The numbers of tandem mass (MS/MS) spectra are shown for the 8 -SH group-containing peptides of water-soluble nuclear βA1/A3-crystallin. A shows total counts for each of the 8 peptides containing an -SH group; B shows peptides containing protein-bound glutathione (PSSG) expressed as per -SH peptide; and C shows peptides containing protein-bound cysteine (PSSC) expressed as per -SH peptide. Open bars are counts from age-matched controls and solid black bars are counts after 30 treatments of the animals with hyperbaric oxygen. There is a different vertical scale for A, compared to those for B and C, which are identical. The counts in A correspond to a soluble protein sample of 0.4 mg. Peptides for each of the 8 cysteine residues in panel A showed an O₂-induced decrease in number of counts. A relatively low number of counts were detected for the C117 control and O₂-treated peptides. The majority of O₂-induced PSSG (B), and to a lesser extent PSSC (C), was shown by residues C142 and C165.