A new chiral ligand exchange capillary electrophoresis system based on Zn(ii)–l-leucine complexes coordinating with β-cyclodextrin and its application in screening tyrosinase inhibitors

Abstract

Tyrosinase plays a key role in melanin formation, and it is closely related to hyper pigmentation in animals and enzymatic browning in food. Thus, it is of great significance to screen inhibitors of tyrosinase. In this work, a new chiral ligand exchange-capillary electrophoresis (CLE-CE) system based on the coordination effect of Zn(II)–L-leucine complexes and β-cyclodextrin (β-CD) was developed for screening the inhibitors of tyrosinase. The effects of the concentration of β-CD, buffer pH, the ratio of L-leucine to Zn(II), and the complex concentration were investigated with Dns-D,L-tyrosine, Dns-D,L-valine and Dns-D,L-phenylalanine as the tested analytes. The optimum buffer conditions were composed of 100.0 mM boric acid, 5.0 mM ammonium acetate, 3.0 mM Zn(II), 6.0 mM L-leucine and 4.0 mM β-CD at pH 8.2. It has been found that six pairs of Dns-D,L-AAs could be baseline-separated and five pairs of Dns-D,L-AAs were partly enantioseparated. Then the quantitative analysis of L-tyrosine was conducted and good linearity (r² = 0.992) was obtained with a concentration ranging from 12.95 μM to 413.3 μM. A kinetics study of tyrosinase was realized, and the K_m and V_max were 636 μM and 312 μmol min⁻¹ mg⁻¹. Moreover, the proposed method was applied in screening the inhibitors of tyrosinase with four kinds of chalcones as the model inhibitors. The results demonstrated that the developed CLE-CE system was favorable for screening enzyme inhibitors, and showed great potential in related drugs discovery and clinical analysis in the future.