Design of a heterogeneous enzymatic catalyst on chitosan: investigation of the role of conjugation chemistry in the catalytic activity of a Laccase from Trametes versicolor

BACKGROUND Three protocols are presented in order to immobilise a laccase (EC 1.10.3.2) from Trametes versicolor on chitosan. In particular, chitosan is functionalized with glutaraldehyde and epichlorohydrin to explore to what extent the conjugation of the enzyme is affected by a carbonyl- or epoxy-modified surface, respectively. In addition, an oxidation procedure is tested to modify, for the first time, the carbohydrate moiety of the enzyme and exploit it for linking with the amine group of chitosan. RESULTS The system in which laccase is directly conjugated to chitosan seems to be the best-performing since it is able to maintain 100% of initial activity over a 30 day period and at least 50% of the starting activity after 3 catalytic cycles. CONCLUSION The methods show the capability to develop three biocatalysts suitable for the immobilization of laccase. All of them provide covalent bonds that don't inactivate the enzyme through any conformational change and any distortion of the active pocket. Specifically, the oxidation procedure proves to be feasible for the preparation of stabilized glycoproteins without the introduction of foreign molecules, suggesting that the carbohydrate moiety of laccase does not appear to be closely related to the catalytic site of the protein. © 2017 Society of Chemical Industry