Ishii Takeshi, Ichikawa Tatsuya, Minoda Kanako, Kusaka Koji, Ito Sohei, Suzuki Yukiko, Akagawa Mitsugu, Mochizuki Kazuki, Goda Toshinao, Nakayama Tsutomu
Department of Food and Nutritional Sciences, and Global Center of Excellence Program, University of Shizuoka, 52-1 Yada, Suruga-ku, Shizuoka 422-8526, Japan.
Biosci Biotechnol Biochem. 2011;75(1):100-6. doi: 10.1271/bbb.100600. Epub 2011 Jan 7.
Human serum albumin (HSA) contributes to the stabilization of (-)-epigallocatechin gallate (EGCg) in serum. We characterize in the present study the mechanisms for preventing EGCg oxidation by HSA. EGCg was stable in human serum or buffers with HSA, but (-)-epigallocatechin (EGC) was unstable. We show by comparing EGCg and EGC in a neutral buffer that EGCg had a higher binding affinity than EGC. This indicates that the galloyl moiety participated in the interaction of EGCg with HSA and that this interaction was of critical importance in preventing EGCg oxidation. The binding affinity of EGCg for HSA and protein carbonyl formation in HSA were enhanced in an alkaline buffer. These results suggest the reversible covalent modification of EGCg via Schiff-base formation, and that the immobilization of EGCg to HSA, through the formation of a stable complex, prevented the polymerization and decomposition of EGCg in human serum.
人血清白蛋白（HSA）有助于血清中（-）-表没食子儿茶素没食子酸酯（EGCg）的稳定。在本研究中，我们对HSA防止EGCg氧化的机制进行了表征。EGCg在含有HSA的人血清或缓冲液中是稳定的，但（-）-表没食子儿茶素（EGC）是不稳定的。我们通过在中性缓冲液中比较EGCg和EGC表明，EGCg比EGC具有更高的结合亲和力。这表明没食子酰基部分参与了EGCg与HSA的相互作用，并且这种相互作用对于防止EGCg氧化至关重要。在碱性缓冲液中，EGCg对HSA的结合亲和力以及HSA中蛋白质羰基的形成均增强。这些结果表明EGCg通过席夫碱形成进行可逆的共价修饰，并且通过形成稳定的复合物将EGCg固定到HSA上，可防止EGCg在人血清中发生聚合和分解。
