Reactions of blue and yellow fungal laccases with lignin model compounds

Laccases of white-rot fungi Panus tigrinus, Phlebia radiata, and Phlebia tremellosa were isolated from cultures grown in liquid media which did not contain lignin and from the cultures grown on wheat straw. The physical and chemical properties of the laccases grown in submerged cultures were typical for blue fungal laccases. The laccases of the same fungi isolated from the solid-state cultures differed from the blue forms by lack of an absorption maximum at 610 nm. The typical blue laccases of P. tigrinus, Ph. radiata, and Ph. tremellosa acquired an ability to oxidize veratryl alcohol and a non-phenolic dimeric lignin model compound of beta-1-type only in the presence of a redox mediator, 2, 2'-azinobis(3-ethylbenzthiazolinesulfonic acid). The P. tigrinus and Ph. radiata yellow laccases catalyzed the oxidation of the same substrates without any mediator. The rate of the reaction of the blue laccases with a phenolic dimeric lignin model compound of beta-O-4-type was higher than that of the yellow laccases. The yellow laccases are apparently formed by the reaction of the blue laccases with low-molecular-weight lignin decomposition products.