Fig. 5. CrPRF is an extremely stable profilin. The stability of CrPRF (circles), HPRO1 (triangles) and ZmPRO5 (diamonds) proteins was determined by incubating them with increasing concentrations of urea and measuring their intrinsic tryptophan fluorescences. The relative fluorescence was plotted against the urea concentration and fitted to a sigmoid curve. For this representative experiment, the denaturation midpoint for HPRO1 was 3.3 M, for ZmPRO5 4.0 M and for CrPRF 5.2 M.