Enantioselectivity of d-amino acid oxidase in the presence of ionic liquids

Abstract

In this paper, enantioselectivities of d-amino acid oxidase (DAAO) in ten ionic liquids were investigated in detail. Among the ionic liquids studied, 3-methylimidazolium formate ([MIM][COO]) was able to trigger enzyme activation with l-Ala as substrate. The enzyme activity of DAAO reached a maximum of 4.26 U mg-1 min-1 in the presence of 40% [MIM][COO], while no activity toward l-Ala was observed when DAAO was incubated with other ILs. Moreover, DAAO activities towards other l-amino acids such as l-Pro and l-Arg were also improved in [MIM][COO], which indicated that the enzymatic enantioselectivity of amino acids was lowered. This was further confirmed by capillary electrophoresis, circular dichrosim and fluorescence analysis. Molecular optimization supported that the protein-ionic liquid interactions modulated the structure of the enzyme, especially in [MIM][COO], leading to relaxation in the enantioselectivity of DAAO. This observation and exploration might open a new window for modulation enantioselectivity resolution in ionic liquids.