Screening of 5′-Methylthioadenosine Nucleosidase Enzyme Inhibitors from Traditional Chinese Medicine and Small Molecular Compounds by Capillary Electrophoresis After Enzymatic Reaction at Capillary Inlet

A capillary electrophoresis (CE) method was developed for the screening of 5′-methylthioadenosine nucleosidase (MTAN) inhibitors in traditional Chinese drugs and small molecular compounds. In this method, reaction occurred at the capillary inlet during a predetermined waiting period, followed by electrophoretic separation of the reaction substrates and products. Parameters affecting separation efficiency and enzyme activity were evaluated systematically. The optimized conditions were as follows: 30 mM phosphate (pH 3.0) running buffer, 25 kV applied voltage, 20 mM HEPES (pH 6.0) reaction buffer, and 4 min incubation time. Under the optimized conditions, the Michaelis–Menten constant ( K m ) of MTAN was 3.44 μM, which agreed with the documented data. The proposed method was successfully applied for MTAN inhibitor screening from 21 natural extracts and 8 small molecular compounds. The results demonstrated the practical applicability of the at-inlet reaction-based CE method in screening of MTAN inhibitors from natural products and small molecular compounds.