Figure 3.

Analysis of Aβ₄₀ species produced by treatment of the AQ series with light exposure by ESI–MS and ESI–MS². (a) ESI–MS spectra of the samples containing Aβ₄₀ and compounds with and without light treatment. The number of red dots represents the number of oxygen atoms incorporated into the Aβ₄₀ monomer [Aβ₄₀ + nO]³⁺ (n = 1, 2, or 3). (b) Sequence of Aβ₄₀ and structures of oxidized His and Met residues. (c, d) ESI–MS² analyses of the singly oxidized peak (m/z = 1448) obtained by treatment of Pur as well as the singly and doubly oxidized peaks (m/z = 1448 and 1453, respectively) generated upon incubation with Alo. In the ESI–MS² studies, monooxidized and dioxidized b and y ions are illustrated in red and green, respectively. Conditions: [Aβ₄₀] = 25 μM; [compound] = 50 μM; 20 mM ammonium acetate (1% v/v DMSO), pH 7.4; 37 °C; 3 h; constant agitation (250 rpm); Kessil lamp (467 nm) for 1 h. The samples were diluted by 5-fold with H₂O before injection into the mass spectrometer.