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Spectroscopic Studies on pH-induced Changes in Secondary Structure of Pophenol Oxidase from Tobacco
Xiao Hourong, Xu Xiaolong, Xie Yongshu, Sheng Liangquan, Zhang Yange, Liu Qingliang*
Department of Chemistry,University of Science and Technology of China,Hefei 230026
Abstract:
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 a-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 a-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 Cu2+ 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.
Key words:  pH,Polyphenol oxidase(PPO),Secondary structure,Spectral transfer
FundProject:
pH诱导烟草多酚氧化酶二级结构变化的光谱学研究
肖厚荣, 徐小龙, 解永树, 盛良全, 张艳鸽, 刘清亮*
中国科学技术大学化学系,合肥 230026
摘要:
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,a-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,归属和讨论了酶活性中心金属离子与配体间全部电荷转移谱带.
关键词:  酸度  多酚氧化酶  二级结构  光谱跃迁
DOI:10.1088/1674-0068/17/2/196-170
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