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Tyrosine hydroxylase activity of immobilized tyrosinase on enzacryl‐AA and CPG‐AA supports: Stabilization and properties

Frog epidermis tyrosinase has been immobilized on Enzacryl‐AA (a polyacrylamide‐based support) and CPGzirclad‐Arylamine (a controlled pore glass support) in order to stabilize the tyrosine hydroxylase activity of the enzyme; in this way, the immobilized enzyme could be used to synthesize L‐dopa from L‐tyrosine. The activity immobilization yield YIMEact (higher than 86%), coupling efficiency (up to 90%), storage stability (no loss in 120 days), and reaction stability (t1/2 was higher than 20 h in column reactors) were measured for tyrosinase after its immobilization. The results showed a noticeable improvement (in immobilization yield, coupling efficiency, and storage and operational stabilities) over previous reports in which tyrosinase was immobilized for L‐dopa production. The activity and stability of immobilized enzyme preparations working in three different reactor types have been compared when used in equivalent conditions with respect to a new proposed parameter of the reactor (Rp), which allows different reactor configurations to be related to the productivity of the reactor during its useful life time. The characteristic reaction inactivation which soluble tyrosinase shows after a short reaction time has been avoided by immobilization, and the stabilization was enhanced by the presence of ascorbate. However, another inactivation process appeared after a prolonged use of the immobilized enzyme. The effects of reactor type and operating conditions on immobilized enzyme activity and stability are discussed.