Fig. 5.

Exposure to ¹O₂ results in loss of the native B2M disulfide bond. MS analysis of the sextuply charged Cys-Cys cross-linked peptide from B2M. Panel A: MS spectrum of the sextuply-charged Cys-Cys cross-linked peptide (m/z 906.59) displaying a +8 Da shift following trypsin digestion in H₂¹⁶O and H₂¹⁸O (1:1 ratio). Panel B: Illumination time-dependent loss of peak area for the Cys-Cys cross-linked peptide from B2M (based on the most intense isotope ion at m/z 907.09 ± 0.02) on photo-oxidation for 5, 15, 30, 60 or 90 min. Data was analyzed by one-way ANOVA with Dunnett's multiple comparison test, and are expressed as a ratio of the control data (native B2M). Panel C: MS/MS spectrum of the sextuply-charged cross-linked peptide showing fragment ions with intensity above 10⁴. Blue b and y ions correspond to the peptide A, while red b and y fragments correspond to peptide B. Spectra were obtained from the software Data Analysis (Bruker), with the fragment ions annotated manually. (For interpretation of the references to color in this figure legend, the reader is referred to the Web version of this article.)