Immobilization of Rhus vernicifera laccase on sepiolite; effect of chitosan and copper modification on laccase adsorption and activity

The enzyme laccase, a multi-copper oxidase found in many plants and fungi, can be used in water treatment processes for the removal of pollutants. Commercially available laccase, derived from Rhus vernicifera, was adsorbed on sepiolite, sepiolite modified with chitosan, sepiolite plus Cu(II), and sepiolite modified with both chitosan and Cu(II) to investigate enzymatic activity. Adsorption of laccase on unmodified sepiolite increased its activity by 250 +/- 40% compared to the non-adsorbed enzyme, whereas for sepiolite-Cu-chitosan and sepiolite chitosan the activity was enhanced by up to 700% and 500%, respectively. The stronger enhancement for the Cu-containing adsorbent suggests that exchangeable Cu has an effect on the adsorbed laccase. Desorption of the adsorbed laccase was < 10%, and the non-desorbed enzyme retained high activity, indicating robust adsorption. This study suggests that chitosan-sepiolite based composites might be used as efficient support for laccase scaffolding and immobilization, thus providing in an effective adsorbent surface for catalytic oxidation of organic pollutants sensitive to laccase activity.