Figure 1.
Metabolite structures and peptide sequences.
1A shows the structures of the reactive metabolites of naphthalene. 1B shows the sequences of the model peptides. Sites of potential adduction by reactive metabolites are circled on the amino acid residues of the sequences.
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.
Table 2.
MS/MS Ion series of unmodified and adduct-modified model peptides by 1,2-naphthoquinone (1,2-NQ) and 1,4-naphthoquinone (1,4-NQ) at pH 8.5.
Table 3.
MS/MS Ion series of diadducted model peptides by naphthoquinones at pH 8.5.
Figure 2.
MS/MS for adduction of peptide GRGDSPC by NDO (m/z 869.3483).
2A shows the possible y- and b-ions associated with MS fragmentation of the peptide adducted on cysteine. 2B shows the MS/MS spectrum of the adducted peptide acquired with labeled ions for designation. Adducted ions are in bold. Fragmentation patterns were the same when incubations were conducted at either pH 7.4 or 8.5.
Figure 3.
MS/MS for adduction of peptide DYKDDDDK by 1,4-NQ (m/z 1171.4366).
3A shows the possible y- and b-ions associated with MS fragmentation of the peptide adducted on lysine. 3B shows the MS/MS spectrum of the adducted peptide acquired with labeled ions for designation. Adducted ions are in bold. Fragmentation patterns were the same when samples were incubated at both pH 7.4 and 8.5.
Figure 4.
Depletion of unadducted peptides by metabolites.
Depletion of GRGDSPC (A), DYKDDDDK (B), and DASFHSWG-NH2 (C) by reaction with either NO (naphthalene epoxide) or NQ (1,2-naphthoquinone) at two different ratios of peptide: metabolite, 1∶1 and 1∶10. Depletion of the unadducted peptide was monitored by measuring the peak area of the peptide at each time point.
Figure 5.
Comparison of peptide binding by metabolite.
Comparison of preferential binding between peptides containing different nucleophilic residues (Cys, Lys, and His) in incubations with NO (A) and NQ (B). Degree of preferential binding was monitored by measuring the peak area of the unadducted peptide ion over time.
Figure 6.
Structures of the predicted adducts.
The products of adduct formation with epoxides were the result of SN2 reactions while the products of adducts formed with naphthoquinones were the result of Michael Addition reactions.
Table 4.
Sites of Adduction.