Abstract
The extracellular laccase (benzenediol: oxygen oxidoreductase, EC 1.10.3.2) of Trametes versicolor was isolated from culture medium and immobilized by entrapment of the enzyme in a solvent-resistant hydrophilic matrix like Sepharose-CL-6B. The gel-enzyme association has been shown to be stable in water containing organic solvents. The efficiency of the immobilized laccase in different organic solvents was comparable with the activity shown in a buffered aqueous system. The immobilized laccase in organic solvents showed a good stability and a high tolerance to elevated temperatures. Water-insoluble organosolv lignin (OL), dissolved in dioxane/water, was readily converted by immobilized laccase from Trametes versicolor. The transformed lignin showed an increase in phenolic groups, changes in the quantity of conjugated elements, and a significant modification of both the aliphatic and aromatic carbon moieties of the lignin molecule. The changes in the lignin molecule were analyzed by UV-, IR-spectroscopy, and 13C-NMR solid-state spectroscopy. High-performance size exclusion chromatography (HPSEC) of the lignin transformed with the laccase—Sepharose complex revealed a pronounced increase in weight-average molecular weight. Polymerization of the lignin in the organic solvent proved to be 4 times more effective than polymerization of the same compound in an aqueous system. Water-insoluble organosolv lignin as well as a variety of lignin-related aromatics, solubilized in dioxane-H 2O (7 : 3), was readily converted by laccase preparation either in batch or in continuous flow column. Reaction of laccase with the solubilized lignin generates in the reaction media reduced oxygen species able to reduce the cytochrome c. For the first time it is now possible to perform enzymatically catalyzed reactions with lignin in an organic solvent. This is a first step towards an enzymatically derivatization of lignin, the formation of polymer blends on the basis of lignin by an enzymatically catalyzed reaction.
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