Thermal stabilities and structural analysis of wild-type, F221A, and F221I SSAPs. (A) Effect of temperature on stability. The values are averages ± standard deviations of three independent experiments. (B) CD spectra of wild-type, F221A, and F221I SSAPs. (C) Fluorescence spectra of wild-type, F221A, and F221I SSAPs. a.u., arbitrary uints.