OXIDATION OF SPRUCE LIGNIN BY FUNGAL LIGNIN PEROXIDASE AND HORSERADISH-PEROXIDASE - COMPARISON OF THEIR ACTIONS ON MOLECULAR-STRUCTURE OF THE POLYMER IN COLLOIDAL SOLUTION

Oxidation of spruce milled-wood lignins in colloidal state catalyzed b y horseradish peroxidase (HRP) and lignin peroxidase (LiP) in the pres ence of H2O2 was compared in nonbuffered dimethylfor mamide/water. Lig nins were characterized for their hydrodynamic properties by size-excl usion chromatography and structural bonding pattern by analysis after thioacidolysis. In contrast to LiP, HRP did not induce modification of lignin hydrodynamic properties. The lignin content in beta-O-4-linked guaiacyl monomers and dimeric structures, however, decreased after ox idation by the two enzymes, indicating large structural changes in the polymer. Preferential degradation by both LiP and HRP of beta-5 and b eta-1 lignin dimeric units was also observed. This suggests a greater susceptibility to enzyme oxidation, as compared to the 5-5' and 4-O-5 lignin substructures. In conclusion, the action of HRP on the lignin p olymer. is similar in many respects to that of fungal LiP, but is dist inctly different in its inability to cause a net destructuring of the macromolecular three-dimensional network.