Structure-Dependent Demetalation Kinetics of Chlorophyll a Analogs under Acidic Conditions
Structure-Dependent Demetalation Kinetics of Chlorophyll a Analogs under Acidic Conditions
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DOI：
10.1111/j.1751-1097.2012.01213.x
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发表时间：
2013-01-01
影响因子：
3.3
通讯作者：
Tamiaki, Hitoshi
中科院分区：
文献类型：
--
作者：
Saga, Yoshitaka;Hirai, Yuki;Tamiaki, Hitoshi
叶绿素（Chl） a及其类似物的脱金属是氧合光合生物的一个重要反应，它在光系统II反应中心产生初级电子受体，对Chl的降解至关重要。从这些角度出发，对4种Chl a类似物3,8-二乙烯基-Chl a （DV-Chl a）、3-devinyl-3-乙基-Chl a （mesoChl a）、132-demethoxycarbonyl-Chl a （pyroChl a）和原叶绿素a （PChl a）在弱酸性条件下的脱金属反应进行了动力学分析，并与Chl a的脱金属动力学进行了比较。三种叶绿素色素脱金属动力学的差异源于乙烯基作为外围取代基与乙基的吸电子能力不同。Chl a中吸电子和同共轭的132-甲氧羰基（Chl a -> pyroChl a）的去除使脱金属动力学加快了两倍。具有卟啉型骨架的PChl a比Chl a表现出更慢的脱金属动力学。Chl a类似物的结构依赖脱金属性质将有助于理解氧光合生物体内的Chl脱金属反应。
Demetalation of chlorophyll (Chl) a and its analogs is an important reaction in oxygenic photosynthetic organisms, which produces the primary electron acceptors in photosystem II reaction centers and is crucial in the Chl degradation. From these viewpoints, demetalation reactions of four Chl a analogs, 3,8-divinyl-Chl a (DV-Chl a), 3-devinyl-3-ethyl-Chl a (mesoChl a), 132-demethoxycarbonyl-Chl a (pyroChl a) and protochlorophyll a (PChl a), were kinetically analyzed under weakly acidic conditions, and were compared with that of Chl a. DV-Chl a exhibited slower demetalation kinetics than did Chl a, whereas demetalation of mesoChl a was faster than that of Chl a. The difference in demetalation kinetics of the three chlorophyllous pigments originates from the electron-withdrawing ability of the vinyl group as the peripheral substituent compared with the ethyl group. Removal of the electron-withdrawing and homoconjugating 132-methoxycarbonyl group in Chl a (Chl a -> pyroChl a) accelerated demetalation kinetics by two-fold. PChl a possessing the porphyrin-type skeleton exhibited slower demetalation kinetics than Chl a. The structure-dependent demetalation properties of Chl a analogs will be useful for understanding in vivo Chl demetalation reactions in oxygenic photosynthetic organisms.