Figure 4.

H-D exchange/MS experiment. Amyloid (α-synuclein) HX labeled by timed exposure to D₂O was dissociated with chemical denaturant at the condition of minimum HX rate (Figure 1), then passed through two immobilized acid protease columns, the proteolytic peptides were roughly resolved by HPLC, and then by on line ESI MS. (a) TIC trace of the HPLC eluant. (b) HPLC eluant was continually scanned by ESI MS, as shown for the eluant region marked in (a) MS results for the peptide ion marked in (b) are shown expanded for the protonated (c) and the partially deuterated (d) condition. Subtraction of the centroid mass of the unlabelled all-H peptide from the D-labeled peptide yields the number of D-labeled sites recovered on each peptide.