Figure 3. Identification of an intramolecular crosslink in the p22^phox subunit of Cyt b.

(3A) Overlaid MALDI spectra for Cyt b tryptic digests following incubation with 5% DMSO for 50 min at room temperature (red) and Cyt b tryptic digests following incubation with a 60-fold molar excess of BS²G-d₀/d₄ for 50 min at room temperature (blue). (3B) Overlaid MALDI spectra for Cyt b tryptic digests following incubation with 5% DMSO for 50 min at room temperature (red) and Cyt b tryptic digests following incubation with a 60-fold molar excess of BS³-d₀/d₄ for 50 min at room temperature (blue). Masses attributed to gp91^phox and p22^phox tryptic peptides are labeled numerically in 3A and 3B, and a possible keratin-derived tryptic peptide is indicated (K) in 3B. The initial mass corresponding to the d_o and d₄ peak families in the p22^phox crosslink is indicated by arrows. Theoretical masses of p22^phox residues 68–85 modified with crosslinking agent are as follows: BS²G-d₀ with His72-2199.15 Da; BS²G-d₄ with His72-2203.17 Da; BS²G-d₀ with Tyr72-2225.15 Da; BS²G-d₄ with Tyr72-2229.18 Da; BS³-d₀ with His72-2241.20 Da; BS³-d₄ with His72-2245.22 Da; BS³-d₀ with Tyr72-2267.20 Da; and BS³-d₄ with Tyr72-2271.22 Da.