红茶萃取物及茶黄素对两类酮酰还原酶的抑制作用

Inhibition of Two Type of β-Ketoacyl Reductase by Black Tea and Theaflavins

利用酶动力学方法测定了50%乙醇红茶萃取物和其主要活性成分茶黄素对存在于动物中的I型脂肪酸合酶的酮酰还原催化中心(KR)和存在于细菌中的II型脂肪酸合酶的酮酰还原酶(FabG)的抑制能力和抑制特征.这两个抑制剂对KR和FabG均有强的可逆抑制和不可逆抑制能力,是KR和FabG的底物NADPH的竞争性抑制剂,并且NADPH可以显著降低它们不可逆失活KR和FabG的速率,表明这两个抑制剂可能作用于两种酮酰还原酶的NADPH结合位点.两个抑制剂对KR和FabG的抑制特征基本一致,表明两种不同进化程度的酮酰还原酶的活性部位很相似.序列同源性分析表明它们有一段同源性很高的序列,可能与活性部位组成有关.因此,通过对FabG的研究能够了解KR活性部位的空间结构.由于抑制能力强和来源丰富,这两个抑制剂具有较高的应用潜力.

Inhibitory activity and character of black tea extract and theaflavins are measured through inhibition kinetics. Based on the kinetics data, both of them are proved to be effective inhibitors of β-ketoacyl reductase of type Ⅰ fatty acid synthase （KR）, which exists in animals and β-ketoacyl reductase of type Ⅱ fatty acid synthase （FabG） ,which exists in bacteria. The two inhibitors exhibit potent reversible and irreversible inhibitory activity on KR and FabG and are competitive inhibitors against NADPH, which is one of substrates of KR and FabG. The presence of NADPH clearly prevents the inactivation of KR and FabG by those two inhibitors. This shows that the inhibitors might act on NADPH binding site of KR and FabG. The consistent inhibitory character of two inhibitors suggests that these two β-ketoacyl reductases with different evaluation degrees possess similar active sites. The homology analysis of amino acid sequence shows that there exists one highly homologous region which may be responsible for the formation of active site located in KR and FabG. Therefore, the conformation of the active site in KR can be understood through the study of FabG. These two inhibitors are promising for practical application because of their potent inhibitory activity and rich sources.