Denaturant-dependent equilibrium folding shows involvement of an intermediate during apoflavodoxin folding, as demonstrated by

<p><a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0045746#pone.0045746-Bollen1" target="_blank">[<b>13</b>]</a><b>.</b> (a) Fluorescence emission intensity of tryptophan detected at 340 nm upon excitation at 280 nm. (b) CD signal at 222 nm. (c) Fluorescence anisotropy data detected with a 335 nm cut-off filter, excitation is at 300 nm. Solid lines in panels a to c are the result of a global fit of a three-state model for equilibrium (un)folding. (d) Normalized population of native (N), off-pathway intermediate (I_off), and unfolded (U) apoflavodoxin molecules as a function of denaturant concentration. Protein concentration is 5.6 µM in 100 mM potassium pyrophosphate, pH 6.0, and data are recorded at 25°C.