Veratryl alcohol-dependent production of molecular oxygen by lignin peroxidase

Veratryl alcohol- and H2O2-dependent production of oxygen by lignin peroxidase isozyme H2 (LiPH2) from Phanerochaete chrysosporium was investigated. Veratryl alcohol oxidation by LiPH2 decreased with increasing concentrations of H2O2 while oxygen evolution increased. The absorption spectrum of the LiPH2 in these experiments indicated that it was in the compound II state. We propose that O2 production results from the one electron oxidation of H2O2 by the veratryl alcohol cation radical to yield superoxide, as the addition of superoxide dismutase stimulated oxygen production. It has been reported previously that oxygen is consumed in reaction mixtures containing lignin peroxidase, H2O2, veratryl alcohol, and oxalate (Popp, J. L., Kalyanaraman, B., and Kirk, T.K. (1990) Biochemistry 29, 10475-10480). In the presence of oxalate, we observed oxygen consumption that was dependent on the H2O2 concentration. The ability of other methoxybenzenes to mediate oxygen production appeared to be related to their redox potential. It was concluded that cation radicals can oxidize H2O2 by one electron which results in the production of superoxide and the evolution of molecular oxygen. Thus, the rates of LiPH2-catalyzed O2 consumption or O2 production are dependent on the relative concentrations of H2O2 and oxalate.