STUDIES OF THE THERMODYNAMICS OF ELECTRON-TRANSFER REACTIONS OF BLUE COPPER PROTEINS

The temperature dependences of the reduction potentials of Pseudomonas aeruginosa azurin, bean plastocyanin, and Rhus vernicifera stellacyanin have been studied, giving ΔH°values of -26, -23, and -17 kcal mol-1 and ΔS°values of -63, -52, and -44 eu, respectively. The results have been interpreted in terms of solvation changes that accompany reduction of the blue copper sites of the three proteins. The deduced order of increasing hydrophobicity of the redox sites is stellacyanin < plastocyanin < azurin, which accords with the decreasing kinetic accessibility found for these proteins in reactions with inorganic complexes. © 1979, American Chemical Society. All rights reserved.