L-DOPA production by immobilized tyrosinase

The production of L-DOPA using L-tyrosine as substrate, the enzyme tyrosina se (EC 1.14.18.1) as biocatalyst, and L-ascorbate as reducing agent for the o-quinones produced by the enzymatic oxidation of the substrates was studi ed. Tyrosinase immobilization was investigated on different supports and ch emical agents: chitin flakes activated with hexamethylenediamine and glutar aldehyde as crosslinking agent, chitosan gel beads, chitosan gel beads in t he presence of glutaraldehyde, chitosan gel beads in the presence of poly-v inylpyrrolidone, and chitosan flakes using glutaraldehyde as crosslinking a gent. The last support was considered the best using as performance indexes the following set of immobilization parameters: efficiency (90.52%), yield (11.65%), retention (12.87%), and instability factor (0.00). The condition s of immobilization on chitosan flakes were optimized using a two-level ful l factorial experimental design. The independent variables were enzyme-supp ort contact time (t), glutaraldehyde concentration (G), and the amount of e nzyme units initially offered (U-C). The response variable was the total un its of enzymatic activity shown by the immobilized enzyme (U-IMO). The opti mal conditions were t = 24 h, G = 2% (v/v), and U-C = 163.7 U. Under these conditions the total units of enzymatic activity shown by the immobilized e nzyme (U-IMO) was 23.3 U and the rate of L-DOPA production rate was 53.97 m g/(L.h).