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Figure 2.
Figure 2. pH-dependence of the amide chemical shift
difference between Ub[1] and Ub[2] for the proximal domain. As
can be seen from this plot, the chemical shift perturbations
(Ub[2] versus Ub[1]) saturate at higher pH, so that in most
amide groups there is practically no (or very small) difference
between the chemical shift perturbations observed at pH 6.8 and
7.5. These data suggest that the closed conformation of Ub[2] is
almost fully populated at pH 7.5. In the case of fast exchange,
the relative population of the closed or open conformations at
the intermediate pH values can then be estimated assuming that
the observed perturbation in the peak position is a weighted
average of the corresponding values for the closed (at pH 7.5)
and open (pH 4.5) conformations. The estimates of the population
of the open conformation obtained for the individual amide
groups at pH 6.8 ranged from less than 1% to 25%, with the mean
value of 15%.
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