DIRECT ELECTROCHEMISTRY OF THE BLUE COPPER PROTEINS PSEUDOAZURIN, PLANTACYANIN, AND STELLACYANIN

Direct electrochemistry of three blue copper proteins, Achromobacter cycloclastes IAM 1013 pseudoazurin, Cucumis sativus plantacyanin, and Rhus vernicifera stellacyanin, is achieved at a glassy-carbon electrode over the pH range 5–11 in the absence of mediators and promoters. The formal potentials E°′ for pseudoazurin, plantacyanin, and stellacyanin are 0.28, 0.32, and 0.18 V (vs NHE), respectively, at pH 6.0. These values are identical with those previously determined by the conventional potentiometric titrations. The three blue copper proteins behave as effectively symmetrical redox systems (ipa, ~ ipc) over the pH range 5–11. However, cathodic and anodic wave peak potentials of the three blue copper proteins show diverse pH dependencies, suggesting that an electron might be passed to and from the copper center via different pathways. The oxidation-reduction processes are almost reversible or quasi-reversible at pH < 10, as indicated by the fairly narrow cathodic and anodic peak separations (ΔEp) of 60-90 mV). At pH >10, ΔEp values begin to increase because of the protein structure change, which is partly reflected in the absorption and ESR spectra. © 1990, American Chemical Society. All rights reserved.