THE EFFECT OF VERATRYL ALCOHOL ON MANGANESE OXIDATION BY LIGNIN PEROXIDASES

The extracellular peroxidase isozymes secreted by the white rot fungus Phanerochaete chrysosporium have been classified as manganese peroxid ases (isozymes H3, H4, H5, and H9) and lignin peroxidases (isozymes H1 , H2, H6, H7, H8, and H10). Recently we reported that Lignin peroxidas e isozyme H2 can also oxidize Mn2+ (Khindaria et al., 1995, Biochemist ry 34, 7773-7779). This Lignin peroxidase isozyme oxidized Mn2+ with b oth of the enzyme intermediates, compound I and compound II, at the sa me rates as manganese peroxidase isozyme H4. The results of single-tur nover kinetic studies have now demonstrated that compound I of the oth er lignin peroxidase isozymes (Hi, H6, H7, H8, and H10) also readily o xidized Mn2+, but that the rate of Mn2+ oxidation by compound II was e xtremely slow. Compound III rapidly formed in the presence of Mn2+, ox alate, and H2O2. However, upon the addition of veratryl alcohol, the r esults indicate that veratryl alcohol served to reduce compound II. Un der such conditions, compound III did not accumulate, and a steady sta te 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 vera tryl alcohol was consistent with a mechanism in which Mn2+ is oxidized by compound I and veratryl alcohol is oxidized by compound II. Theref ore, 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 oxi dant. (C) 1996 Academic Press, Inc.