Table 1. MS/MS Ion series of unmodified and adduct-modified model peptides by naphthalene epoxide (NO) and naphthalene diol epoxide (NDO) at pH 8.5.
| Peptide | Modification | Precursor m/z [M+H]+ | b/y-ions detected a | SupplementalFigure Ref. b |
| GRGDSPC | NO c | 835.34 | 386.18 (b4), 473.21 (b5), 450.17 (y3 # ), 565.20 (y4 # ), 691.28 ([M+H]+- X d),817.33 ([M+H]+- H2O) | 1 |
| GRGDSPC | NDO e | 869.31 | 271.15 (b3), 386.17 (b4), 473.21 (b5), 570.26 (b6), 656.21 (y5 ψ ), 812.32 (y6 ψ ),691.28 ([M+H]+- X), 851.32 ([M+H]+- H2O) | Figure 2 |
| GRGDSPC | unmodified | 691.28 | 214.13 (b2), 271.15 (b3), 386.18 (b4), 473.21 (b5), 570.26 (b6), 306.11 (y3),634.26 (y6) | 1 |
| YGGFLRKR | NO | N/A | Precursor mass was not detected. No fragmentation. | N/A |
| YGGFLRKR | NDO | 1174.64 | 872.43 (b6 ψ ), 1000.53 (b7 ψ ), 776.49 (y6), 833.51 (y7), 996.57 ([M+H]+- X),1156.62 ([M+H]+- H2O) | 5 |
| YGGFLRKR | unmodified | 996.57 | 538.26 (b5), 694.37 (b6), 712.38 (b6+ H2O), 822.46 (b7), 840.47 (b7+ H2O),303.21 (y2) | 5 |
| DYKDDDDK | NO | 1139.45 ([M+H]+- H2O) f | 752.27 (b6), 648.26 (b4 # – H2O), 763.29 (b5 # – H2O), 878.32 (b6 # – H2O), 1011.36 (b7 # ), 377.17 (y3), 492.19 (y4), 607.22 (y5) | 2 |
| DYKDDDDK | NDO | 1191.47 | 1045.36 (b7 ψ ), 492.19 (y4), 607.22 (y5), 913.38 (y6 ψ ), 1076.44 (y7 ψ ),1013.41 ([M+H]+- X), 1173.45 ([M+H]+- H2O) | 6 |
| DYKDDDDK | unmodified | 1013.41 | 407.19 (b3), 522.22 (b4), 637.25 (b5), 752.27 (b6), 867.30(b7), 377.17 (y3),492.19 (y4), 607.22 (y5), 735.33 (y6), 898.38 (y7) | 2,6 |
| DASFHSWG-NH2 | NO | 1049.45 | 702.29 (b5 # ), 789.32 (b6 # ), 975.40 (b7 # ), 629.28 (y4 # ), 776.35 (y5 # ), 863.38 (y6 # ), 934.42 (y7 # ), 905.39 ([M+H]+- X), 1031.43 ([M+H]+- H2O) | 3 |
| DASFHSWG-NH2 | NDO | 1083.45 | 736.29 (b5 ψ ), 823.32 (b6 ψ ), 1009.40 (b7 ψ ), 663.29 (y4 ψ ), 810.35 (y5 ψ ), 897.39 (y6 ψ ), 968.42 (y7 ψ ), 905.39 ([M+H]+- X), 1065.44 ([M+H]+- H2O) | 7 |
| DASFHSWG-NH2 | unmodified | 905.39 | 558.23 (b5), 645.26 (b6), 831.34 (b7), 485.22 (y4), 719.33 (y6), 790.36 (y7) | 3,7 |
| EFYAPWCG | NO | 1116.50 | 606.26 (y4 # ), 840.36 (y6 # ), 972.39 ([M+H]+- X), 1098.43([M+H]+- H2O) | 4 |
| EFYAPWCG | NDO | 1150.46 | 794.35 (b6), 640.24 (y4 ψ ), 711.28 (y5 ψ ) 874.34 (y6 ψ ), 1021.41 (y7 ψ ), 1132.43 ([M+H]+- H2O) | 8 |
| EFYAPWCG | unmodified | 972.39 | 511.22(b4), 608.27 (b5), 794.35 (b6), 897.36 (b7), 462.18 (y4), 533.22 (y5),696.28 (y6) | 4,8 |
| EIVRDIKE | NO | N/A | Precursor mass was not detected. No fragmentation. | N/A |
| EIVRDIKE | NDO | N/A | Precursor mass was not detected. No fragmentation. | N/A |
| EIVRDIKE | unmodified | 1001.56 | 498.30 (b4),613.33 (b5), 854.51 (b7), 983.55 ([M+H]+ – H2O – X) | 14 |
Product ion spectra for adducted peptides were indistinguishable between both pH conditions; more products were observed at pH 8.5 therefore ions series for the products at this pH was given.
a
Observed signals assigned as b- or y- ions are listed. The bold b- and y- ions represent ions modified by the naphthalene epoxides.
b
Reference to detailed supplemental spectra corresponding to the appropriate ion series.
c
The modifications are naphthalene epoxide (mass +144.06 Da).
d
In the fragment ion signals, X represents the mass of the adduct.
e
The modifications are naphthalene diol epoxide (mass +178.06 Da).
f
[DYKDDDDK + NO] was observed in the dehydrated form; fragmentation confirmed the adduct.