ELECTROCHEMICAL PROPERTIES OF SOME COPPER-CONTAINING OXIDASES

The electrochemical behaviour of copper-containing oxidases (two lacca ses, tyrosinase, ceruloplasmin and ascorbate oxidase) has been investi gated at graphite and carbon electrodes. These enzymes catalyse the ox idation of organic and inorganic substrates by molecular oxygen in hom ogeneous solutions. Molecular oxygen is reduced directly to water in a four-electron mechanism. Direct (mediatorless) bioelectrocatalysis of oxygen reduction was observed with electrodes modified with fungal an d lacquer tree laccase. It was found that when the electrode modified with fungal laccase was used oxygen electroreduction started at a pote ntial approximately 0.35 V more positive than that observed with the e lectrode modified with lacquer tree laccase, The effect of different p retreatments of the electrode surface before adsorption of laccase was investigated. It was established that the optimum pH for the electroc atalytic reaction of oxygen reduction in the presence of lacquer tree laccase is shifted towards the alkaline range compared with that with fungal laccase. No redox transformations of the prosthetic groups of t he two laccases were revealed in anaerobic conditions and in the prese nce of various promoters. No bioelectrocatalytic reaction of oxygen wa s revealed with the other oxidases, An electrochemical response was ob tained at electrodes coated with only tyrosinase or ceruloplasmin in t he absence of oxygen, The conditions which can influence the bioelectr ocatalysis have been discussed.