Laccase electrochemistry

Figures 5.4 and 5.5 summarize results of a recent study of P. versicolor laccase electrochemistry based on cyclic and rotating disk voltammetry [60]. Figure 5.4 shows unequivocally that this laccase is voltammetrically active and gives a kinetically controlled, unpromoted four-electron peak at edge-plane pyrolytic graphite. Electrochemical reduction of 02 catalyzed by an immobilized laccase monolayer is close to reversible, and unrestricted by mass transport. The electrocatalysis follows, moreover, a Michaelis-Menten pattern (Fig. 5.5). Finally, there is a characteristic bell-shaped functional pH-profile with a pronounced maximum at pH 3.1.

Laccase, 36 318, 329, 40 122 see also Blue copper oxidases amino-acid sequences, 40 141 anaerobic reduction, 40 158-160 biological function, 40 124 electrochemistry, 36 360 fungal, 40 145-152 evolution, 40 153-154 inhibition, 40 162 kinetic properties, 40 157-162 molecular and spectroscopic properties, 40 125-126... 

The first accounts that seemed to give direct enzyme electrochemistry were the reports concerning a soluble blue Cu oxidase, laccase, which catalyzed the rapid four-electron reduction of dioxygen to water. An efficient electrocatalysis of O2 reduction by adsorbed fungal laccase on pyrolytic graphite, glassy carbon, and C02-treated carbon black electrodes was first described by Tarasevich and co-workers (48). Several control experiments were carried out to verify direct electron transfer from the electrode to the Cu sites of the enzyme. 

Y.B. (2008) Direct electrochemistry of laccase immobilized on au nanoparticles encapsulated-dendrimer bonded conducting polymer application for a catechin sensor. Analytical Chemistry, 80 (21), 8020-8027. 

The actual diameter of an object d) smaller than the tip radius has an imaged diameter (D) when the radius of the tip (r) and the height Qi) are considered. Hence, the apparent enzyme diameter of 26 nm, calculated to be an actual radius of 4.5 nm for the enzyme, is in close agreement with an enzyme monolayer thickness of 8nm calculated from force measurements and the reported diameter of the T. versicolor laccase [67]. From values of the observed electric current and electrode surface area (measured by direct electrochemistry and capacitance analysis, respectively) and the enzyme density calculated from the average area per enzyme molecule derived from AFM height images, the current per enzyme molecule was calculated to be 5xlO pA. 

Zheng W, Zhou HM, Zheng YF, Wang N. A comparative study on electrochemistry of laccase at two kinds of carbon nanotubes and its application for biofuel cell. Chem Phys Lett 2008 457 381-385. 

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