Figure 1.

Electrospray ionization-MS of (a) protonated Aβ monomer, (b) protonated Aβ fibrils, (c) deuterated Aβ monomer in deuterated solvent, and (d) deuterated Aβ monomer in protonated solvent. The protein sample and processing solution were pumped through two arms of the T at flow rates of 2 μl/min and 18 μl/min, respectively. The final concentration of Aβ monomer was 2.9 μM, and the equivalent concentration of monomers from fibrils was ≈1.1 μM. Several charge states were obtained but only the +6 charge state is shown here for clarity. The average molecular mass (corrected by subtracting the mass of ionizing protons or deuterons) calculated by using data from +6 and +5 charge states is indicated for each sample.