Figure 3 - Unfolding transition of trypsinogen in 100 mM MES, pH 7.0, 20 mM CaCl2 and 81 mM NaNO3, pH 7.0, as a function of urea concentration. The fraction fU was calculated from the molar ellipticity at 300 nm from circular dichroism (circles) and from difference spectroscopy signal at 293 nm (triangles). The near-UV CD was monitored at 300 nm using a 0.5-cm path length cuvette. The difference spectroscopic measurements were made in a 0.5-cm path length tandem cell as described in the procedures. Protein concentration was 1 mM for each sample and temperature 25oC. The dashed line represents a two-state fit of the CD 300-nm data calculated according to Santoro and Bolen (24). The solid line represents the two-state fit of DS 293-nm data. The statistical analysis of the data is presented in Table 1.