ANISALDEHYDE AND VERATRALDEHYDE ACTING AS REDOX CYCLING AGENTS FOR H2O2 PRODUCTION BY PLEUROTUS-ERYNGII

The existence of a redox cycle leading to the production of hydrogen p eroxide (H2O2) in the white rot fungus Pleurotus eryngii has been conf irmed by incubations of 10-day-old mycelium with veratryl (3,4-dimetho xybenzyl) and anisyl (4-methoxybenzyl) compounds (alcohols, aldehydes, and acids). Veratraldehyde and anisaldehyde were reduced by aryl alco hol dehydrogenase to their corresponding alcohols, which were oxidized by aryl-alcohol oxidase, producing H2O2. Veratric and anisic acids we re incorporated into the cycle after their reduction, which was cataly zed by aryl-aldehyde dehydrogenase. With the use of different initial concentrations of either veratryl alcohol, veratraldehyde, or veratric acid (0.5 to 4.0 mM), around 94% of veratraldehyde and 3% of veratryl alcohol (compared with initial concentrations) and trace amounts of v eratric acid were found when equilibrium between reductive and oxidati ve activities had been reached, regardless of the initial compound use d. At concentrations higher than 1 mM, veratric acid was not transform ed, and at 1.0 mM, it produced a negative effect on the activities of aryl-alcohol oxidase and both dehydrogenases. H2O2 levels were proport ional to the initial concentrations of veratryl compounds (around 0.5% ), and an equilibrium between aryl-alcohol oxidase and an unknown H2O2 -reducing system kept these levels steady. On the other hand, the conc omitant production of the three above-mentioned enzymes during the act ive growth phase of the fungus was demonstrated. Finally, the possibil ity that anisaldehyde is the metabolite produced by P. eryngii for the maintenance of this redox cycle is discussed.