Figure 4. Electrospray ionization (ESI) mass spectral analysis of A2E irradiated (430 nm, 20 min) in the absence (A) and presence (B) of glutathione (GSH). A2E, m.w. 592, 200 μM; GSH, 10 mM. A: The series of peaks at 592 <m/z <736 reflect A2E photooxidation products (592 + n*16, n=1, 2…9). Lower mass peaks (<m/z 592) correspond to A2E photocleavage products. B: The peaks at 592 < m/z <738 exhibit m/z+2 relative to A2E photooxidation products in A. The series of peaks at m/z 931, 947, 963, 979, 995, 1011, 1027, and 1043 are photooxoA2E-GSH adducts (mechanisms of formation are proposed in Figure 6). Insets in A and B: expanded view in range of m/z 850–1100. Note that the y-axis scale is magnified in B to facilitate resolution.