Lignin peroxidase compound III. Formation, inactivation, and conversion to the native enzyme

At pH 3.0 in the absence of a reducing substrate and the presence of only 20 equivalents of H₂O₂, lignin peroxidase (LiP) is readily converted to LiP compound III (LiPIII) (Fe(III)O^-₂ - complex). LiPIII which is produced via the reaction of LiP compound II (LiPII) with H₂O₂ is not part of the peroxidase catalytic cycle, and is readily and irreversibly inactivated. Veratryl alcohol (VA), a Phanerochaete chrysosporium secondary metabolite, protects the enzyme from inactivation via two mechanisms. Acting as a substrate, VA reduces LiPII to regenerate the native enzyme. Secondly, the binding of VA to LiPIII rapidly displaces O^.-₂/HO^.-₂, thereby converting LiPIII directly to the native enzyme. VA is not consumed during this displacement reaction. These results help to explain the role of VA in stabilizing the enzyme in the presence of excess H₂O₂.