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Enzymology of Kraft Pulp Bleaching by Trametes versicolor

1996; American Chemical Society; Linguagem: Inglês

10.1021/bk-1996-0655.ch011

1947-5918

Michael G. Paice, Frederick S. Archibald, Robert Bourbonnais, L. Jurášek, Ian D. Reid, Trevor C. Charles, Tim Dumonceaux,

Lignin and Wood Chemistry

Trametes versicolor and other white-rot fungi can lower the residual lignin content (kappa number) and increase brightness of kraft pulps without diminishing the pulps' strength or yield. Experiments with 14C-labelled lignin indicate that the residual lignin is solubilized but not extensively mineralized by T. versicolor. Laccase, manganese peroxidase (MnP) and cellobiose dehydrogenase (CDH) are produced by the fungus during bleaching, but based on molecular modelling studies, they are unable to freely access residual lignin in the kraft pulp fibre wall. Two isozymes of laccase were purified and compared: both enzymes required a mediator such as ABTS for pulp delignification, and under optimum conditions could produce up to 55% lignin removal. However, several lines of evidence indicate that MnP is the key enzyme required for fungal bleaching. CDH has several potential roles in delignification, including generation of complexing agents and Mn(II) for MnP.