HIGH-POTENTIAL STATES OF BLUE AND PURPLE COPPER PROTEINS

Electrochemical measurements show that there are high-potential states of two copper proteins, Pseudomonas aeruginosa azurin and Thermus the rmophilus Cu-A domain; these perturbed states are formed in guanidine hydrochloride (GuHCl) solution in which the proteins are still blue (a zurin) and purple (Cu-A). In each case, the high-potential state forms reversibly. Absorption (azurin, Cu-A), visible circular dichroism (az urin, CUA) resonance-Raman (Cu-A), and EPR (CUA) spectra indicate that the structure of the oxidized copper site of each high-potential form is very similar to that of the native protein. It is proposed that Gu HCl perturbs one or more H-bonds in the blue or purple copper active s ite, thereby allowing Cu(I) to adopt a more favorable coordination str ucture than that in the rigid cavity of the native protein. (C) 1998 E lsevier Science B.V. All rights reserved.