(A) Fluorescence emission scan of DrPCP3b following excitation at 280 nm in buffer containing zero urea (red) or 8 M urea (blue). (B) Fluorescence emission scan of DrPCP3b following excitation at 295 nm in buffer containing zero urea (red) or 8 M urea (blue). (C) Circular dichroism (CD) far-UV scan of DrPCP3b in buffer containing zero urea (red) or 8 M urea (blue). (D) Representative equilibrium unfolding/folding of DrPCP3b at pH 7 by fluorescence emission (average emission wavelength) following excitation at 280 nm (), 295 nm (), and CD at 224 nm (). Refolding data for fluorescence emission (280 nm (▲) and 295 nm (▼)) and CD (◣) show that folding is reversible. Solid lines represent global fits to a three-state folding model, as described in the text.