Proteins can exist in one of two states, the active, folded state and the inactive, unfolded state. Protein folding is sometimes thought of as a first-order phase transition from folded to unfolded (denaturation) with increasing temperature. (We will revisit this description in Chapter 15.) Denaturation is accompanied by an increase in molecular volume and a significant positive latent heat (i.e.,Δ_F→_DV > 0 and _F→_DH > 0).

a. Sketch the Gibbs energy function for both D (denatured) and F (folded) proteins, and identify T^∗, the phase transition temperature. Which state has the higher entropy? 

b. Given the observed volume and enthalpy changes upon denaturation, how would increasing the pressure affect T^∗? Should biopharmaceuticals (i.e., folded proteins) be stored under high pressure?