Colloids and surfaces. B, Biointerfaces | 2021
High efficiency of osmotically stable laccase for biotransformation and micro-detoxification of levofloxacin in the urea-containing solution: Catalytic performance and mechanism.
Abstract
Laccase-catalyzed oxidation was applied in the biotransformation of levofloxacin (a potentially environmental antibiotic contamination); however, the enzyme may denature in urea-containing wastewater and lead to the formation of an inactive form followed by decreasing the yield of the bio-removal. In this study, the osmolytes-stabilized laccase was used to eliminate levofloxacin in the urea-containing solution. Sorbitol and proline 100 mM appeared to be the two most efficient laccase protectants against the urea-induced denaturation. In a 1-M urea solution, the maximum velocity (Vmax) of laccase was estimated to be 39.1 μmol min-1 mg-1. This value was improved to 101.7 and 51.8 μmol min-1 mg-1 in the presence of sorbitol and proline, respectively. In optimal conditions for the elimination of levofloxacin, sorbitol- and proline-treated laccase led to 82.9 % and 76.2 % bio-removal of the applied fluoroquinolone in 1 M urea solution, respectively. Biotransformation products of the parent antibiotic were spectroscopically analyzed that assigned to different reaction pathways including demethylation, defluorination, decarboxylation, deamination, and hydroxylation. A micro-toxicity study concerning the growth of some Gram+ and Gram- bacteria exhibited decreasing in inhibition of laccase-treated levofloxacin after a 10-h incubation at 37 °C.