四川边茶提取物对脂肪酸合酶的抑制作用

Inhibitory effects of Sichuan brick tea extracts on fatty acid synthase

四川边茶(康砖)是黑茶的一个主要品种,所含茶多酚与绿茶和红茶不同.本研究利用酶动力学方法测定了边茶萃取物对脂肪酸合酶(Fatty Acid Synthase,FAS,E.C.2.3.1.85)的抑制作用,近几年研究报道该酶是减肥和抑癌的双重潜在靶点.结果表明,边茶萃取物对FAS有可逆和不可逆抑制双重作用,最佳萃取溶剂为50%的乙醇,在常温下5h即可达到最佳萃取效果.用开水泡茶的方法经两次浸取可提取出近60%的抑制FAS有效物,比绿茶的浸出效率约高1倍,但需较长的浸泡时间.边茶的新茶对脂肪酸合酶的抑制能力并不强,存放数年的边茶抑制能力最好,其后有所下降,但大部分抑制活性可保持20年以上,而30年以上保存期可能会使抑制能力明显下降.边茶提取物与底物乙酰辅酶A和丙二酸单酰辅酶A的竞争性质都是竞争性与非竞争性的混合型;对FAS中的酮酰还原反应的抑制不明显,这说明酮酰还原酶结构域并不是其主要作用位点;这些和绿茶及红茶都有不同.由实验结果分析边茶中的抑制剂不同于红茶和绿茶,可能是茶多酚中的茶褐素,其抑制能力高于儿茶素而接近茶黄素.这些结果表明边茶在减肥、抑癌等方面可能具有良好的应用前景.

Sichuan brick tea （Kang Zhuan） contains different tea polyphenols from those of green tea and black tea. The inhibition on Fatty acid synthase （ E. C. 2.1.3.85, FAS） by the extracts of brick tea is measured by inhibition kinetics. FAS has been reported as a potential new therapeutic target for both cancer and obesity. The results show that the inhibition included both reversible and irreversible processes. The optimal solvent for extracting FAS inhibitors is 50% ethanol. The extraction was achieved during 5 h in room temperature. The boiling water could extract about total 60% effective FAS inhibitors by two times extraction. The final efficiency is two-folds of that for green tea, but longer time is needed for the extraction. The inhibition of FAS by new brick tea was not stronger, and brick tea stored for several years showed the best inhibitory activity. More storage time led to a reduction in the inhibitory ability of brick tea. Howere, most of that ability can be maintained for over 20 a. It is seems that the storage over 30 a markedly weakened the ability of brick tea. The brick tea extracts inhibited the overall reaction of FAS in a mixed manner of competitive and noncompetetive with acetyl-CoA and malonyl-CoA. It inhibited the ketoacyl reduction of FAS weakly, which indicated that the ketoacyl reductase domain is not the main reacted site that brick tea extracts attracted. These results shows that the inhibitor in brick tea is different from that in green tea and black tea. It is proposed that the effective element in brick tea should be theabrownine （TB）, whose inhibitory ability is higher than that of catechins and is close to that of theaflavins. The results exhibited prospects of brick tea for fat-reducing and anti-cancer applications.