Production of L-DOPA by tyrosinase immobilised on zeolite membrane

3,4-dihydroxyphenyl-L-alanine (L-DOPA) is an effective drug in the treatment of Parkinson's disease, a neurological disorder which has a great impact in elderly people [1]. Today, this drug is chemically produced according to Monsanto process [2], but its synthesis suffers of disadvantages such as the presence of multiple reaction steps and the use of expensive and not eco-friendly chiral catalysts. In this context, many efforts were devoted to study alternative routes for the drug synthesis. Some investigations focussed on the microbiological production of L-DOPA from Erwinia herbicola [3] and Escherichia coli [4]. However, the need for the purification steps for removing proteins and metabolic by-products, produced by these micro-organisms, and the low concentration of the drug in the product stream increase the cost of the microbial synthesis, making it economically unfeasible. A promising approach is the enzymatic conversion of the L-tyrosine by using the tyrosinase (EC. 1.14.18.1) [5]. Poor enzyme stability and its easy inactivation due to mechanical stress by stirring, high cost for purification of both enzyme and product from the reaction medium are the main drawbacks of these systems. Enzyme immobilization leads to the increase of enzyme stability and its re-use in successive reaction cycles, lowering the total production cost. Different papers dealt with the immobilization on polymeric membranes [6, 7]. In the present work, for the first time, the production of L-DOPA using a zeolite membrane bioreactor was studied. This approach combines the active role of the zeolite membrane in supporting the enzyme and for blocking free radicals generated during the reaction. Besides, the possibility of an easy membrane regeneration when the biocatalyst became exhaust was investigated. FAU zeolite supported membranes were prepared by secondary growth method. Tyrosinase immobilised on the zeolite membrane exhibited good performance in terms of specific activity and productivity. Comparing the performance of the tyrosinase free in solution and immobilized on zeolite membrane, it can be observed that the enzyme specific activity in the latter case is 2.76 times higher than the first one (1.93 ?mol mg-1 min-1 and 0.70 ?mol mg-1 min-1, respectively). Furthermore, it was also s higher than the values present in the open literature. The experimental results show as the thermal treatment, carried out burning the organic materials, did not change the properties of the zeolite membranes.