对羟基肉桂酸对酪氨酸酶催化反应的抑制机理

本文研究了对羟基肉桂酸(HCA)对酪氨酸酶催化单酚底物L-酪氨酸和催化二酚底物L-多巴的抑制能力,并利用紫外-可见光谱、荧光光谱以及分子对接技术探究了其抑制机理。结果表明对羟基肉桂酸对酪氨酸酶催化单酚底物L-酪氨酸比催化二酚底物L-多巴具有更强的抑制作用,半抑制浓度分别为0.096 mmol/L和0.500 mmol/L;紫外-可见分析发现对羟基肉桂酸能与Cu2+发生螯合,使光谱发生明显红移。进一步通过荧光光谱分析得到,对羟基肉桂酸在酪氨酸酶溶液中并没有出现荧光淬灭反而随着对羟基肉桂酸浓度的增大荧光强度变强,说明对羟基肉桂酸被酪氨酸酶催化氧化成对应的醌类物质。利用分子对接技术揭示了对羟基肉桂酸通过氢键和疏水作用竞争性地占据了单酚和二酚底物的空间位置,并与酪氨酸酶中双核铜离子螯合,从而抑制酪氨酸酶催化L-酪氨酸和L-多巴氧化的活性机理。

Inhibition Mechanism of 4-Hydroxycinnamic Acid on Reactions Catalyzed by Tyrosinase

The purpose of this study was to investigate the inhibition effect of 4-hydroxycinnamic acid (HCA) on the catalytic activity of tyrosinase on the monophenol substrate L-tyrosine and diphenol substrate L-dopa. The mechanism of inhibition was studied using UV-vis spectroscopy, fluorescence spectroscopy, and molecular docking. The results showed that HCA was more effective at inhibiting the catalytic activity of tyrosinase on the diphenol substrate L-tyrosine than on the monophenol substrate L-dopa; their IC50 values were 0.096 and 0.500 mmol/L, respectively. The UV-visible spectrum showed a red shift in the characteristic absorption peak of HCA because of the formation of a Cu2+ chelate complex. Furthermore, fluorescence quenching of HCA in tyrosinase solution did not occur and instead, the fluorescence intensity increased with increasing HCA concentration, indicating that HCA was catalytically oxidized to the corresponding quinone by tyrosinase. Molecular docking demonstrated that HCA could competitively occupy the positions of both monophenol and diphenol substrates in the active site of tyrosinase by hydrogen bonds and hydrophobic interaction, and could coordinate to Cu2+ in tyrosinase, thus inhibiting the catalytic activity of tyrosinase on L-tyrosine and L-dopa oxidation.