Chlorophylls b and c: Why plants make them
Chlorophylls b and c: Why plants make them
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叶绿素 b 和 c：植物为何产生它们
DOI：
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发表时间：
2004
期刊：
影响因子：
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通讯作者：
J. Hoober
中科院分区：
文献类型：
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作者：
Laura L. Eggink;R. Lobrutto;J. Hoober
植物中捕光复合物的稳定性需要通过将Chla的7-甲基氧化成7-甲酰基来合成叶绿素（Chl）B。甲酰基的吸电子性质使分子电子密度向大环的外围重新分布，远离中心Mg，这增加了金属的刘易斯酸“硬度”。因此，更强的配位键形成与“硬”路易斯碱配体，如羧基和氧诱导的偶极酰胺基团，配体是相对不利的协调与叶绿素a，在脱辅基蛋白的捕光复合物。Chl a被Chl a加氧酶氧化为Chl B。的EPR谱的酶揭示信号的单核铁和铁-硫复合物，这是预测的氨基酸序列，也为一个稳定的自由基的氨基酸，可能是酪氨酸。Chl c的共轭环π系统通过反式丙烯酸酯侧链的双键延伸到未酯化的负电性羧基，在有色藻类中起着与Chl B在植物中相同的作用。
Stability of light-harvesting complexes in plants requires synthesis of chlorophyll (Chl) b by oxidation of the 7-methyl group of Chl a to the 7-formyl group. The electron-withdrawing property of the formyl group redistributes the molecular electron density toward the periphery of the macrocycle, away from the central Mg, which increases the Lewis acid 'hardness' of the metal. Consequently, stronger coordination bonds are formed with 'hard' Lewis-base ligands, such as carboxyl groups and the oxygen-induced dipole of amide groups, ligands that are relatively unfavorable for coordination with Chl a, in the apoproteins of the light-harvesting complexes. Chl a is oxidized to Chl b by Chl a oxygenase. The EPR spectrum of the enzyme revealed signals for a mononuclear iron and an iron-sulfur complex, which are predicted by the amino acid sequence, and also for a stable radical on an amino acid, possibly a tyrosine. Chl c, in which conjugation of the ring π system extends through the double-bond of the trans-acrylate side-chain to the unesterified, electronegative carboxyl group, serves the same role in chromophytic algae as Chl b does in plants.