Ligninase-catalyzed hydroxylation of phenols
1989
Schmall, M.W. | Gorman, L.S. | Dordick, J.S.
Lignin peroxidase (ligninase) catalyzes the hydroxylation of phenols in the presence of dihydroxyfumarate and molecular oxygen at pH 4 with a turnover number of 1.7 s-1. After 3 h, 50% of a 2 mM phenol solution reacts to give catechol and hydroquinone in a respective ratio of 4.5:1. The hydroxylase and dihydroxyfumarate oxidase reactions are strongly uncoupled; 10-fold more dihydroxyfumarate is oxidized, presumably to diketosuccinate, than phenol is hydroxylated. This hydroxylation reaction is distinct from all other reported reactions involving ligninase, in that hydrogen peroxide is not involved as the external oxidant. Hence the chemistries associated with ligninase compounds I and II are not involved in the hydroxylation rea ction, although this cannot be ruled out for dihydroxyfumarate oxidation. Instead, superoxide and hydroxyl radicals are involved in the hydroxylation and ligninase compound III is an active intermediate. Phenol hydroxylation, therefore, is the first reported catalytically active role for ligninase compound III. In addition to phenol, p- and m-cresols, and L-tyrosine are also hydroxylation substrates.
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