Direct heterogeneous electron transfer reactions of Bacillus halodurans bacterial blue multicopper oxidase

Direct electron transfer reactions of Bacillus halodurans bacterial multicopper oxidase on bare spectrographic graphite, as well as bare and thiol-modified gold electrodes were studied using cyclic voltammetry, potentiometry, amperometry, and spectroelectrochemistry. The redox potential of the T1 site of the enzyme was measured using mediatorless redox titration and found to be 325 mV +/- 10 mV vs. NHE. From measurements with a mercaptopropionic acid-modified gold electrode under aerobic conditions a midpoint potential of 360 mV vs. NHE for the T2/T3 copper cluster is deduced. Differing from most other characterized laccases of fungal and plant origins this bacterial enzyme exhibits bioelectrocatalytic activity at neutral pH and tolerates high chloride concentrations (200 mM), conditions that usually strongly inhibit catalysis. Moreover, it has the very high affinity towards molecular oxygen both in solution and in the adsorbed state (K-M <= 50 mu M).