Fig. 3.

Acceleration by urea of I_trap folding to the native state (○). Data for re-folding of M under the same conditions (37 °C, 10 mM Mg²⁺) are included for comparison (∇, data from ref. 10). Across the range of urea concentrations shown for measurements of I_trap folding, the rate constant was much larger than that for re-folding of M, allowing a robust determination of the rate constant for the transition from I_trap to the native state. At higher urea concentrations (1–2 M), these rate constants become more similar to each other, as shown by the convergence of the lines, such that only the re-folding of M can be measured accurately.