Fig. 2.

Thermodynamics of unlabeled VPK. The first derivative of the absorbance with respect to temperature ($\delta A/\delta T$), from measurements on unlabeled VPK (SI Appendix, Fig. S1 A and B), is plotted as a function of temperature (blue). Measurements were done in 10 mM 3-(N-morpholino)propanesulfonic acid buffer (pH 7.0) at 50 mM KCl. The data (▲) are the averages of two to three independent sets of measurements; the errors are the SEM. The continuous black line is a fit to a three-state model, with transitions at 46.6 ± 0.4 °C and 85.5 ± 0.3 °C. The heat capacity of VPK at 50 mM obtained from simulations is shown in cyan, with transitions observed at 47 °C and 84 °C.