Production of hydroxyl radical by the synergistic action of fungal laccaseand aryl alcohol oxidase

A mechanism for the production of hydroxyl radical (. OH) during the oxidat ion of hydroquinones by laccase, the ligninolytic enzyme most widely distri buted among white-rot fungi, has been demonstrated. Production of Fenton re agent (H2O2 and ferrous ion), leading to OH formation, was found in reactio n mixtures containing Pleurotus eryngii laccase, lignin-derived hydroquinon es, and chelated ferric ion. The semiquinones produced by laccase reduced b oth ferric to ferrous ion and oxygen to superoxide anion radical (Oz) Dismu tation of the latter provided the H2O2 for OH generation. Although O-2(.-) could also contribute to ferric ion reduction, semiquinone radicals were th e main agents accomplishing the reaction. Due to the low extent of semiquin one autoxidation, H2O2 was the limiting reagent in Fenton reaction. The add ition of aryl alcohol oxidase and 4-methoxybenzyl alcohol (the natural H2O2 -producing system of P. eryngii) to the laccase reaction greatly increased OH generation, demonstrating the synergistic action of both enzymes in the process. (C) 2000 Academic Press.