FE unfolding curves for two fusions with increasing GuHCl. For Ub71L (a) and Ub71h (b). GuHCl concentrations: solid circles 0.0 M, open circles 0.2 M, solid squares 0.5 M, open squares 1 M, solid triangles 1.6 M, open triangles 2.6 M, solid diamonds 3.6 M, open diamonds 4.5 M. Spectra were also taken in 6 M GuHCl (not shown). (c) Fraction unfolded was calculated by dividing total observed red shift by the red shift at each denaturant concentration. Data are given for Ub71L attached to ubiquitin (solid circles) and cleaved from ubiquitin (open circles) and for Ub71h attached to ubiquitin (solid squares).