THERMODYNAMIC APPROACH TO COLD DENATURATION OF PROTEINS

Treatment of protein unfolding in aqueous solutions as a thermodynamic equilibrium involving water molecules provides connections between water activity and low and high temperature unfolding points, here indicated as T(L) and T(H). Given the dome shape of the Gibbs energy difference DELTA-N(D)G between native and denatured protein in the (T(L), T(H)) range, the corresponding trends of entropy DELTA-N(D)S and heat capacity DELTA-N(D)C(p) variations are consequently drawn; the latter remains positive throughout this range and shows an upward parabolic behaviour with a minimum at some intermediate temperature T(m) where the entropy change shows a flexus and becomes zero. The former is negative for T < T(m) and becomes positive for T > T(m). Simple expressions are reported for routine estimations of T(L), T(m) and the native versus denatured stability, with comparison between calculated and experimental data.