The effect of veratryl alcohol on manganese oxidation by lignin peroxidase

The extracellular peroxidase isozymes secreted by the white rot fungus Phanerochaete chrysosporium have been classified as manganese peroxidases (isozymes H3, H4, H5, and H9) and lignin peroxidases (isozymes H1, H2, H6, H7, H8, and H10). Recently we reported peroxidase isozyme H2 can also oxidize Mn2+ (Khindaria et al., 1995, Biochemistry 34, 7773-7779). This lignin peroxidase isozyme oxidized Mn2+ with both of the enzyme intermediates, compound I and compound II, at the same rates as manganese peroxidase isozyme H4. The results of single-turnover kinetic studies have now demonstrated that compound I of the other lignin peroxidase isozymes (H1, H6, H7, H8, and H1O) also readily oxidized Mn2+, but that the rate of Mn2+ oxidation by compound II was extremely slow. Compound III rapidly the presence of Mn2+, oxalate, and H2O2. However, upon the addition of veratryl alcohol, the results indicated that veratryl alcohol served to reduce compound II. Under such conditions, compound III did not accumulate, and a steady-state rate of Mn2+ oxidation was observed. The rate of Mn2+ oxidation was the same as for the reduction of compound II by veratryl alcohol. The dependence of the rate of Mn2+ oxidation on the concentration of veratryl alcohol was consistent with a mechanism in which Mn2+ is oxidized by compound I and veratryl oxidized by compound II. Therefore, under physiologically relevant conditions, in which both veratryl alcohol and Mn2+ are present, all lignin peroxidase isozymes would be capable of oxidizing Mn2+ to Mn3+ which can serve as a diffusible oxidant.