FIGURE 4.

Variation of r_H (black) and ellipticity at 222 nm (red) with sodium perchlorate concentration in the presence of 0 m urea (a), 1 m urea (b), 3 m urea (c), and 4 m urea (d). At low urea concentration (0 and 1 m urea), the formation of I_C and I_S are not simultaneous. In the presence of high concentration of urea (3 and 4 m urea), however, I_C and I_S form simultaneously. The variation of r_H with sodium perchlorate concentration in the absence of urea (a) could be fit successfully using a two-state unfolding transition. The data deviate from this model in the presence of urea and the drawn lines are only for presentation purposes (b–d).