Mikhail Yu. Balakshin, Chen-Loung Chen, Josef S. Gratzl, Adrianna G. Kirkman, Harald Jakob
Kinetic Studies on Oxidation of Veratryl Alcohol by Laccase-Mediator System. Part 1. Effects of Mediator Concentration
Summary
Kinetics of the laccase-catalyzed oxidation of veratryl alcohol with dioxygen in the presence of 2,2?-Azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diamonium salt (ABTS), the mediator, were studied
to elucidate the possible reaction mechanism and the role of the mediator in this reaction. The reaction
follows a pseudo-first order reaction law. The first order rate constant (?) is dependent on the Mediator/Substrate (M/S) ratio and has a maximum at M/S molar ratio of 0.15. The kinetic studies show
that the mechanism of veratryl alcohol oxidation with dioxygen-laccase-ABTS is rather complex and
includes different reaction pathways. The mediator is involved in competitive reactions. It has been suggested
that at low mediator concentration, the veratryl alcohol is oxidized via the laccase redox cycle.
The mediator acts mostly as a laccase activator at a M/S ratio lower than 0.15. With increasing ABTS
concentration with respect to the substrate concentration, ABTS acts increasingly as a cosubstrate competing
with the original substrate for active centers of the laccase. This results in inhibition of veratryl
alcohol oxidation in the enzyme cycle and increases the role of substrate oxidation by an oxidized
mediator.
Holzforschung, Walter de Gruyter
Print ISSN: 0018-3830
Volume: 54, 02/2000
Pages: 165 - 170
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