The pH-dependent redox inactivation of amicyanin from Paracoccus versutus as studied by rapid protein-film voltammetry.

Journal article

The redox properties of the blue copper protein amicyanin have been studied with slow and fast scan protein-film cyclic voltammetry. At slow scan rates, which reveal the thermodynamics of the redox reactions, the reduction potential of amicyanin depends on pH in a sigmoidal manner, and the data can be analysed in terms of electron transfer being coupled to a single protonatable group with pKa(red)=6.3 and pKa(ox) < or = 3.2 at 22 degrees C. Voltammetry at higher scan rates reveals the kinetics and shows that the low-pH reduced form of amicyanin is not oxidised directly; instead, oxidation occurs only after conversion to the high-pH form. Simulations show that this conversion, which gates the electron transfer, occurs with a rate constant >750 s-1 at 25 degrees C. In order to decrease the rate of the coupled reaction, the experiments were performed at 0 degrees C, at which the rate constant for this conversion was determined to be 35 +/- 20 s-1. Together with evidence from NMR, the results lead to a mechanism involving protonation and dissociation of the copper coordinating histidine-96 in the reduced form.

Authors: Jeuken, L; Camba, R; Armstrong, F; Canters, G

• Publication status: Published
• Journal: Journal of biological inorganic chemistry : JBIC : a publication of the Society of Biological Inorganic Chemistry
• Volume: 7
• Issue: 1-2
• Pages: 94-100
• Publication date: 2002-01-01
• DOI: 10.1007/s007750100269
• EISSN: 1432-1327
• ISSN: 0949-8257
• Language: English
• Keywords: Thermodynamics; Copper; Kinetics; Paracoccus; Electron Transport; Potentiometry; Hydrogen-Ion Concentration; Bacterial Proteins; Histidine; Oxidation-Reduction; Metalloproteins; Magnetic Resonance Spectroscopy