pH诱导烟草多酚氧化酶二级结构变化的光谱学研究

Spectroscopic Studies on pH-induced Changes in Secondary Structure of Pophenol Oxidase from Tobacco

为了获得更多的关于多酚氧化酶二级结构和活性中心结构的信息 ,应用FT -IR以及去卷积技术、荧光光谱、紫外差光谱研究了溶液 pH的变化对烟草多酚氧化酶的二级结构的影响并对其活性中心的光谱跃迁进行了归属 .实验结果表明 ,随着 pH值的降低或提高 ,多酚氧化酶的二级结构发生了变化 ,浕 螺旋和反平行 β 折叠含量减少 ,无规卷曲含量有所增加 ,同时色氨酸和酪氨酸残基的微环境发生了一定的变化 ;随pH的降低 ,活性中心的Cu2 + 与配位的组氨酸咪唑基的作用加强 ;此外 。

In order to obtain that more information on the secondary and active site structure of polyphenol oxidase from nicotinan tobacco, FT-IR, synchronous fluorescence and Vis-UV have bee employed to study the secondary structure changes of polyphenol oxidase induced by pH. The results show that, compared with native PPO(pH=7), PPO at pH=2 contains less both ɑ-helix and anti-parallel β-sheet, more random coil, and almost the same amount of β-turn, and that PPO at pH=11 contains less ɑ-helix , anti-parallel β-sheet, β-turn, and more random coil. The microenvironments of both Trp and Tyr residues in PPO undergo some changes with pH changing. With the decrease in pH values at the range of pH=7.0～3.38, the coordination between Cu 2+ in the active site and imidazoles of histidine are strenghtened. Different LMCT bands of the PPO active site have been observed by changing pH, which result from the structure of Cu(Ⅱ)-imidazole and Cu(Ⅱ)-imidazolate.