| Abstract
| - The oxidation of phenolic oligomers by lignin and manganese peroxidases was studied bytransient-state kinetic methods. The reactivity of peroxidase intermediates compound I and compound IIwas studied with the phenol guaiacol along with a β-O-4 phenolic dimer, trimer, and tetramer. CompoundI of both peroxidases is much more reactive than compound II. The rate constants for these substrateswith Mn peroxidase compound I range from 1.0 × 105 M-1 s-1 for guaiacol to 1.1 × 103 M-1 s-1 for thetetramer. Reactivity is much higher with lignin peroxidase compound I with rate constants ranging from1.2 × 106 M-1s-1 for guaiacol to 3.6 × 105 M-1 s-1 for the tetramer. Rate constants with compound IIare much lower with Mn peroxidase exhibiting very little reactivity. The rate constants dramaticallydecreased with both peroxidases as the size of the substrate increased. The extent of the decrease wasmuch more dramatic with Mn peroxidase, leading us to conclude that, despite its ability to oxidize phenols,Mn2+ is the only physiologically significant substrate. The rate decrease associated with increasing substratesize was more gradual with lignin peroxidase. These data indicate that whereas Mn peroxidase cannotefficiently directly oxidize the lignin polymer, lignin peroxidase is well suited for direct oxidation ofpolymeric lignin.
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