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.

aProduct 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. Observed signals assigned as b- or y- ions are listed. The bold b- and y- ions represent the adduct-modified ions by the naphthoquinones.bReference to detailed supplemental data spectra corresponding to the appropriate ion series.cThe modifications are 1,2-naphthoquinone (mass +158.04).dThe adducted masses were observed from peptide-metabolite incubations performed at both pHs; spectra obtained from products formed at pH 8.5 are given.eIn the detected fragment ion signals, X represents the mass of the adduct.fThe modifications are 1,4-naphthoquinone (mass +158.04).g,h,iThe spectrum for these unmodified peptides are referenced to in the supplemental figures for the epoxide adducts, not the quinone adducts.