Bioelectrocatalytic and Enzymic Activity of Laccase in Water–Ethanol Solutions

The effect the composition of a water–ethanol mixture has on the enzymic (in the pyrocatechol oxidation reaction) and bioelectrocatalytic in a broad potential range (in the oxygen reduction reaction) activity of laccase (L) is studied. On the basis of obtained results conclusions are made about the influence exerted by ethanol in the composition of the water–ethanol mixture on the activity of laccase solubilized and immobilized in the composition of a composite (laccase–Nafion). The decrease in the activity in both the enzymic and the bioelectrocatalytic reactions is probably caused by the denaturation of laccase, which is due to the replacement of the hydration shell of a protein globule by a solvation shell. Besides, there take place a retardation of the kinetic stage of the formation of a laccase–substrate complex (LHO2OH) because of the slowness of the diffusion of water into an active center and an inhibiting effect of ethanol, which is capable of binding itself to an enzyme globule in the vicinity of the active center of laccase.