FIGURE 4.

SAXS data as a function of Na⁺ concentration in the absence of glycine. (A) Scattering profiles of the VCI-II aptamer in Kratky representation (q^2.I as a function of q) in the presence of 50, 100, 150, 300, 550, 800, 1050, and 2050 mM Na⁺, color coded from blue (low Na⁺) to red (high Na⁺). (B) VCI-II radii of gyration (black symbols) obtained from Guinier fits to scattering data (left axis R_g² in Ų, right axis R_g in Å) as a function of total Na⁺ concentration and the Hill fit to the data (black solid line). The errors are obtained from Guinier fits with slightly different fitting ranges. (Inset) Fractional population of the M state (f_M) from two-state projections of the SAXS scattering profiles and the corresponding Hill fit to the data (solid lines).