REDOX THERMODYNAMICS OF BLUE COPPER PROTEINS

The thermodynamic parameters of protein reduction (ΔH°‘rc and ΔS°‘rc) were measured for a number of blue copper proteins including spinach plastocyanin, cucumber plastocyanin, Pseudomonas aeruginosa azurin, Rhus vernicifera stellacyanin, cucumber stellacyanin, and horseradish umecyanin through voltammetric techniques in nonisothermal experiments at neutral pH. Including previous estimates for other members of the same protein family, we discuss here the thermodynamics of the electron-exchange reaction for twelve blue copper proteins from different sources. The enthalpic term (-ΔH°‘rc/F) turns out to be the dominant contribution to the reduction potential in this protein class. However, the entropic term (TΔS°‘rc/F) heavily affects E°‘, especially for the azurins. These data were analyzed in the light of the structural and dynamic information available on protein folding, geometric and electronic features of copper ligation, and solvation properties of the two redox states. It is clearly seen that the redu...