Investigations on the reduction of molecular oxygen on polyphenol oxidase-modified electrode

Polyphenol oxidase (PPO, E.C.1.10.3.1) from Nicotiana tobacum, PPO II, shows a different behavior from that of PPOs from other sources. A one-electron oxygen reduction on PPO II Nafion modified glassy carbon electrode surface has been observed by square-wave voltammetry. The cathodic peak has been found to be proportional to the concentration of dissolved oxygen. The optimum salt concentration was 0.2 mol/l. The study of its dependence on pH (4-9) indicates that the reduction of oxygen is accompanied by a one-proton-transfer process. Temperature shows little influence on the cathodic peak. The electrode storage has also been studied to evaluate its stability.