Use of cross-linked tyrosinase aggregates as catalyst for synthesis of l-DOPA

Mushroom tyrosinase immobilized as cross-linked enzyme aggregates (CLEAs) was used as the catalyst for production of l-3,4-dihydroxyphenylalanine (l-DOPA) from l-tyrosine. The synthetic reaction catalyzed by this immobilized enzyme was investigated in different processes. In the batch process, a conversion of 53.0% was obtained during 2 h with a productivity of 209.0 mg l−1 h−1, much superior to other batch processes catalyzed by the same enzyme immobilized with traditional carrier-bound immobilization methods. The effects of pH, temperature, and l-ascorbic acid (as the reducing agent) on the l-DOPA production were examined. Reactions can be tracked by determining the l-DOPA concentration with the spectrophotometric and HPLC methods, both giving consistent results as long as the reducing agent is in sufficient supply. In the continuous synthetic processes carried out in a continuous stirred-tank reactor and a packed bed reactor, a productivity of 103.0 and 48.9 mg l−1 h−1 was obtained, respectively. The operational stability of the tyrosinase CLEAs can be dramatically improved by entrapment into calcium alginate gels. The CLEA/alginate beads in the continuous stirred-tank reactor achieved a long life time of >104 h, producing l-DOPA with a productivity of 57.4 mg l−1 h−1.

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► Mushroom tyrosinase can be immobilized as cross-linked enzyme aggregates (CLEAs).
► Tyrosinase CLEAs efficiently catalyze the production of l-DOPA from l-tyrosine.
► High productivity can be obtained in both batch and continuous flow processes.
► Operability of CLEAs is remarkably enhanced by entrapment into Ca alginate gels.