Fig. 2.

The results of pulse–quench H-to-D exchange of intact TmIGPS after a 9 d equilibration is displayed at selected GdnHCl concentrations. The normalized +28-charge state (solid black curves) was fitted with a pair of Gaussian functions to account for the presence of two intermediates (solid brown and green curves). The dotted lines show the deuterium uptake for native (violet) and unfolded (red) states. Residuals for the fitting curves are shown as dash-dot-dot black lines. The implied limits for the exchange reactions, EX1 and EX2, are indicated. A 10 s deuterium pulse was required to fully exchange the backbone NHs with the longest intrinsic exchange lifetime (∼3 s) as determined with program SPHERE (20).