Pre-steady state kinetic studies on the microsecond time scale of the laccase from Trametes versicolor

Laccase from Trametes versicolor reduces dioxygen to water. The enzyme is used in green chemistry applications such as the selective oxidation of alcohols in the presence of a suitable mediator (TEMPO) or in biofuel cells. We studied the catalytic mechanism of the enzyme by the stopped-flow and our newly developed rapid-mixing rapid sampling method, which has an experimental dead time of 75 +/- 15 mu s. Equilibrium and kinetic analyses yielded a reduction potential of 717 +/- 5 mV for Type 1 copper center. EPR and low-temperature UV-Vis spectroscopy indicate that oxidation of the blue copper center and O=O bond splitting occur within 100 mu s, without detectable formation of a peroxide intermediate. These results indicate a rapid internal electron transfer between the various copper centers (> 25.000/s) and rapid binding of O-2 (k(on) > 5 x 10(7) M-1 s(-1)). Mechanistic aspects of the catalytic cycle are shortly discussed. (C) 2007 Elsevier B.V. All rights reserved.