Simultaneous purification and immobilization of Aspergillus niger xylanase on the reversibly soluble polymer EudragitTM L-100

The non-covalent immobilization of a commercial preparation of xylanase from A. niger was carried out on a reversibly soluble-insoluble enteric polymer EudragitTM L-100. The immobilization of the xylanase activity by adsorption was simultaneously accompanied by removal of cellulase activity since the latter did not bind to the polymer. Thus, the soluble enzyme derivative may be useful for treatment of paper pulp bleaching in paper industry. The immobilized xylanase retained 60% of its activity toward xylan as the substrate. No change was observed in the pH optimum (5.5) of the enzyme upon immobilization. Only marginal increase in the Km of the free enzyme (3.6 mg ml−1 to 5.0 mg ml−1) upon immobilization on the soluble polymer reflected that the enzyme-substrate binding continues to be efficient in spite of the macromolecular nature of the substrate. Fluorescence spectroscopy and UV difference spectroscopy were used to probe the change(s) in the enzyme structure upon immobilization. This change in structure was correlated with the “effectiveness factor” of the enzyme activity. CD spectra also showed that the enzyme undergoes drastic changes in the structure.