Fig. 4.
MSn analysis of DSSO heterodimeric interlinked peptide of cytochrome c (α-β: HKTGPNLHGLFGR interlinked to GKK). This peptide was detected in MS as triply charged [α-β]3+ (m/z 641.67303+), quadruply charged [α-β]4+ (m/z 481.50694+), and quintuply charged [α-β]5+ (m/z 385.40705+) ions. A, MS/MS spectrum of [α-β]3+ (m/z 641.67303+) in which two fragment pairs were observed: αA (m/z 744.402+)/βT (m/z 418.21) and αT (m/z 760.382+)/βA (m/z 386.24). B, MS/MS spectrum of [α-β]4+ (m/z 481.50694+) in which two fragment pairs were observed: αA (m/z 496.603+)/βT (m/z 418.21) and αT (m/z 507.263+)/βA (m/z 386.24). C, MS/MS spectrum of [α-β]5+ (m/z 385.40705+) in which two fragment pairs were observed: αA/βT (m/z 496.603+/209.612+ and 372.704+/418.21) and αT (m/z 507.263+)/βA (m/z 193.622+). D, MS3 spectrum of αA fragment (m/z 496.603+) in which detection of a series of y and b ions determined its sequence unambiguously as HKATGPNLHGLFGR. KA is modified with the alkene moiety.