Production of L-DOPA by tyrosinase immobilized on modified polystyrene

Mushroom tyrosinase was immobilized on modified polystyrene- polyamino styrene (PSNH) and polymethylchloride styrene (PSCL)-to produce L-DOPA from L-tyrosine. Glutaraldehyde was used as an activating agent for the PSNH to immobilize the tyrosinase, and 10% (w/v) glutaraldehyde was optimal in conferring the highest specific activity (11.96 U/g) to the PSNH. Methylchloride on the PSCL was directly linked with the tyrosinase, and 1.5 mmol of Cl/g was optimal in attaining the specific activity of 17.0 U/g. The temperature and optimal acidity were, respectively, 60 degrees C and pH 5.5 for the PSNH, and 70 degrees C and pH 3.0 for the PSCL. In a 50-mL batch reactor working over 36 h, the L-DOPA production rate at 30 degrees C was 1.44 mg/(L x h) for the PSNH and 2.33 mg/(L x h) for the PSCL. The production rate over 36 h was 3.86 mg/(L x h) for the PSNH at 60 degrees C and 5.54 mg/(L x h) for the PSCL at 70 degrees C. Both of the immobilized enzymes showed a remarkable stability with almost no change in activity after being stored wet. The operational stability study indicated a 22.4% reduction in L-DOPA production for the PSNH and an 8.63% reduction for the PSCL over seven runs (each run was for 144 h at 30 degrees C) when the immobilized enzymes were used under turnover conditions. The immobilized tyrosinase was more stable on the PSCL than on the PSNH.