Effect of various pollutants and soil-like constituents on laccase from Cerrena unicolor

Laccase from Cerrena unicolor catalyses the oxidation of a wide range of ar omatic compounds, either xenobiotic or naturally occurring phenols, leading to the formation of polymeric products. These are characterized by their l ow solubility and often may form precipitates or aggregates. The oxidizing efficiency of the enzyme is strictly dependent on the number of hydroxyl gr oups and the position of substituents on the phenolic molecules. During the reaction with some substrates, the enzyme is inactivated, because of possi ble adsorption of laccase molecules on newly formed polyphenols. By contras t, the oxidation of humic precursors (i.e., resorcinol, gallic acid, and py rogallol) does not influence greatly the residual laccase activity. The tri azinic herbicides, triazine and prometryn (2,4-bis (isopropylamino)-6-methy lthio-s-triazine), are not substrates of laccase, They, however, inhibit la ccase activity assayed with 2,4-dichlorophenol (2,4-DCP) or catechol as sub strates. The reduction of substrate oxidation rates is usually accompanied by the retention of higher levels of residual enzymatic activity. These res ults, together with the slight recovery in laccase activity following dialy sis of the assay mixture, provide further evidence that the enzyme may be i ncorporated into or adsorbed onto polyphenolic products, with a consequent reduction in the concentration of active forms of laccase.