Title
PH-Dependent Enantioselectivity of D-amino Acid Oxidase in Aqueous Solution
Author
Qingju Liu, Li Chen, Zhikun Zhang, Bibai Du, Yating Xiao, Kunhao Yang, Lingling Gong, Li Wu, Xiangjun Li, Yujian He
Year
2017
Journal
Scientific Reports
Abstract
D-amino acid oxidases (DAAO) are stereospecific enzymes which are generally almost inactive towards L-enantiomer in neutral solution when L-, D-amino acids are supplied as substrates. In this paper, the D-amino acid oxidase can catalytic oxidize L-amino acids by modulating pH of aqueous solution. With L-Pro as substrate, the catalytic rate (kcat) and the affinity (Km) of DAAO were 6.71s−1 and 33mM at pH 8.0, respectively, suggesting that optimal pH condition enhanced the activity of DAAO towards L-Pro. Similar results were obtained when L-Ala (pH 9.8), L-Arg (pH 6.5), L-Phe (pH 9.0), L-Thr (pH 9.4), and L-Val (pH 8.5) were catalyzed by DAAO at various pH values. The racemization of the L-amino acids was not found by capillary electrophoresis analysis during oxidation, and quantification analysis of L-amino acids before and after catalytic reaction was performed, which confirmed that the modulation of enantioselectivity of DAAO resulted from the oxidation of L-amino acids rather than D-amino acids by changing pH. A mechanistic model was proposed to explain enhanced activity of DAAO towards L-amino acids under optimal pH condition.
Instrument
J-815
Keywords
Circular dichroism, Secondary structure, Chemical stability, Biochemistry