Reduction potentials of blue and purple copper proteins in their unfolded states: a closer look at rack-induced coordination

Abstract

Cyclic voltammetry has been used to determine the reduction potentials of blue (Pseudomonas aeruginosa azurin) and purple (Thermus thermophilus CuA domain) copper proteins unfolded by guanidine hydrochloride. These Cu(II/I) potentials [456 (azurin); 453 (CuA) mV vs., NHE] are higher than those of the folded proteins. The downshift of the potential in the folded state can be accounted for by assuming that rack-induced axial coordination stabilizes Cu(II) relative to Cu(I) in a protein-encapsulated active site.