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. Author manuscript; available in PMC: 2008 Feb 25.
Published in final edited form as: J Biol Chem. 2007 Jan 24;282(13):9335–9345. doi: 10.1074/jbc.M608589200

FIGURE 4. MALDI-TOF-Q-TOF mass spectrometry of samples digested overnight with endoproteinase Asp-N at 37°C.

FIGURE 4

A, unmodified Aβ42 (5 μM). The three fragments expected from N-side cleavage at Asp-6 and Asp-22 are evident at m/z 774, 1871, and 1906. Other ions present are discussed in the text. B, Aβ42 (5 μM) treated with excess HNE (3.8 mM) in the presence of 2.5 mM DMPC and 50 μM Aβ-(16 –20). An ion at m/z 930 corresponds to Aβ-(1– 6) that has shifted 156 atomic mass units by Michael addition of HNE. Treatment with HNE also produced multiple ions between m/z 2000 and 2200, with several corresponding to the addition of 138, 156, 138, + 156 = 294, and 156 + 156 = 312 atomic mass unit to the ion at m/z 1906. The ion at m/z 1871 is unchanged by HNE treatment. Similar data were obtained following the digestion of Aβ40 with and without HNE treatment (data not shown).