Tyrosinase@HKUST-1: A Super Stable Biocatalyst Efficient for Catecholic Product Synthesis

Although metal-organic frameworks (MOFs) have been considered as promising matrices for enzyme immobilization, HKUST-1, constructed from copper acetate (CuAc2) and benzene 1,3,5-tricarboxylate (BTC), has rarely been explored for this application. In this study, mushroom tyrosinase (EC 1.14.18.1) was immobilized in the form of tyrosinase@HKUST-1 following a simple reaction procedure we developed. The order of mixing BTC with the enzyme prior to addition of CuAc2 is believed to be responsible for the super stability exhibited by the immobilized enzyme so formed. The resultant biocatalyst was characterized in both structural features and catalytic properties. Upon incorporation into the HKUST-1 frameworks, the enzyme gained a prominent enhancement in stability against pH, temperature and storage: When incubated at 50 oC and pH 6.0, tyrosinase@HKUST-1 presented a half-life of 32.6 h, which is 77-fold and over 10-fold higher than that of the free enzyme and its other immobilization forms, respectively; and the catalyst fully maintained its activity for at least 2 months when stored at 30 oC. The applicability of this new biocatalyst was demonstrated by employing it as catalyst for regioselective ortho-hydroxylation reactions to produce catecholic products with huge pharmacological effects, i.e., hydroxytyrosol and L-DOPA, with excellent yields and productivities. This study has thus offered a facile immobilization method to prepare a novel biocatalyst with super stability, and tyrosinase@HKUST-1 so formed from crude mushroom extract provides an efficient catalyst which can be applied to the production of catecholic products with health benefits.