Laccases from basidiomycetes: Physicochemical characteristics and substrate specificity towards methoxyphenolic compounds

Laccases from the Basidiomycetes Coriolus hirsutus, Coriolus Zonatus, Cerre na maxima, and Coriolisimus ful-vocinerea have been isolated and purified t o homogeneity and partially characterized. The kinetics of oxidation of dif ferent methoxyphenolic compounds by the fungal laccases has been studied. A s laccase substrates, such methoxyphenolic compounds as 4-hydroxy-3,5-dimet hoxycinnamic acid (sinapinic acid), 4-hydroxy-3-methoxycinnamic acid (ferul ic acid), and 2-methoxyphenol (guaiacol) were used. The stoichiometries of the enzymatic reactions were determined: guaiacol and sinapinic acid are on e-electron donors and their oxidation apparently results in the formation o f dimers. It was established that k(cat)/K-m, which indicates the effective ness of catalysis, increases in the series guaiacol, ferulic acid, and sina pinic acid. This fact might be connected with the influence of substituents of the phenolic ring of the substrates. This phenomenon was established fo r fungal laccases with different physicochemical properties, amino acid com position, and carbohydrate content. This suggests that all fungal laccases possess the same mechanism of interaction between organic substrate electro n donors and the copper-containing active site of the enzyme and that this interaction determines the observed values of the kinetic parameters. rs.