Figure 1.

(A) Reversible unfolding transitions of PrP(121–231) at 22°C in the presence of urea at pH 4.0 (▾), 4.5 (▪), 5.0 (⧫), 6.0 (▴), and 7.0 (•). (A) Mean residue ellipticities at 222 nm. The solid lines result from fitting the data according to a two-state model for pH 5.0, pH 6.0, and pH 7.0 and according to a three-state model for pH 4.0 and pH 4.5. The corresponding refolding experiments are represented by open symbols. (B) Three-state analysis of the fractions of the native (▵), intermediate (•), and unfolded state (□) of PrP(121–231) at pH 4.0.