Exploring the catalase activity of unspecific peroxygenases and the mechanism of peroxide-dependent heme destruction

The catalase activity of three unspecific peroxygenases (UPOs) from the agaric basidiomycetes Agrocybe aegerita, Coprinopsis cinerea and Marasmius rotula was investigated. The study included analysis of pH dependency of the catalase reaction and H2O2 mediated enzyme inactivation as well as experiments on the influence of a second substrate on the course of catalase reaction. Apparent kinetic parameters (Km, kcat) for the catalase activity of UPOs were determined. Inactivation of UPOs by H2O2 is discussed with regard to O2 production and remaining UPO activity. Furthermore formation of biliverdin as heme destruction product was demonstrated along with the formation of UPO compound III as a possible intermediate that forces the destruction process. Radical trapping experiments with methyl benzoate gave indication for the formation of hydroxyl radicals in the presence of excess H2O2. Eventually, a plausible pathway of heme destruction has been proposed, proceeding via UPO compound III and subsequent hydroxyl radical formation, which in turn may cause heme bleaching and verdoheme and biliverdin formation.