Characterization of tyrosinase for the treatment of aqueous phenols

Abstract

Mushroom tyrosinase (polyphenol oxidase, EC 1.14.18.1) was investigated as an alternative to peroxidase enzymes for the catalytic removal of phenolic compounds from wastewaters. Maximum catalytic activity was observed at pH 7 and more than 50% of optimum activity was observed at pHs ranging between 5 and 8. Tyrosinase was unstable under acidic conditions and at elevated temperatures. The activation energy for thermal inactivation of tyrosinase at pH 7 was determined to be 1.85 kJ mol −1 using l-tyrosine as a substrate. Phenol was successfully transformed by tyrosinase over wide ranges of pH 5–8 and initial phenol concentration (0.5–10 mM, 47–940 mg/l). Several chlorinated phenols were also successfully transformed. Polyethylene glycol and chitosan did not protect tyrosinase from inactivation during the treatment of phenol; however, chitosan induced the precipitation of reaction products arising from phenol transformation.