Effect of redox state on unfolding energetics of heme proteins

Both the enthalpic and entropic contributions to unfolding of three heme proteins, cytochrome b(562), cytochrome c and myoglobin, are larger for the reduced than for the oxidized form. Thus, the higher thermodynamic stability of a reduced, as compared to an oxidized, heme protein is the net result of a large increase of favorable enthalpy and a small increase in unfavorable entropy. Upon comparing the unfolding energetics of the heme proteins to those of other single-domain proteins I find that protein length is the primary determinant of the thermodynamics.