OXIDATION OF GUAIACOL BY LIGNIN PEROXIDASE - ROLE OF VERATRYL ALCOHOL

We have investigated the Lignin peroxidase-catalyzed oxidation of guai acol and the role of veratryl alcohol in this reaction by steady-state and pre-steady-state methods. Pre-steady-state kinetic analyses demon strated that guaiacol is a good substrate for both compounds I and II, the two- and one-electron oxidized enzyme intermediates, respectively , of Lignin peroxidase. The rate constant for the reaction with compou nd I is 1.2 x 10(6) M(-1) s(-1). The reaction of guaiacol with compoun d II exhibits a K-d of 64 mu M and a first-order rate constant of 17 s (-1). Oxridation of guaiacol leads to tetraguaiacol formation. This re action exhibits classical Michaelis-Menten kinetics with a K-m of 160 mu M and a k(cat) of 7.7 s(-1). Veratryl alcohol, a secondary metaboli te of ligninolytic fungi, is capable of mediating the oxidation of gua iacol. This was shown by steady-state inhibition studies. Guaiacol com pletely inhibited the oxidation of veratryl alcohol, whereas veratryl alcohol had no corresponding inhibitory effect on guaiacol oxidation, In fact, at low guaiacol concentrations, veratryl alcohol stimulated t he rate of guaiacol oxidation. These results collectively demonstrate that veratryl alcohol can serve as a mediator for phenolic substrates in the lignin peroxidase reaction.