Vavilin Dmitrii, Vermaas Wim
School of Life Sciences and Center for the Study of Early Events in Photosynthesis, Arizona State University, Box 874501, Tempe, AZ 85287, USA.
Biochim Biophys Acta. 2007 Jul;1767(7):920-9. doi: 10.1016/j.bbabio.2007.03.010. Epub 2007 Apr 3.
Chlorophyll synthesis and degradation were analyzed in the cyanobacterium Synechocystis sp. PCC 6803 by incubating cells in the presence of 13C-labeled glucose or 15N-containing salts. Upon mass spectral analysis of chlorophyll isolated from cells grown in the presence of 13C-glucose for different time periods, four chlorophyll pools were detected that differed markedly in the amount of 13C incorporated into the porphyrin (Por) and phytol (Phy) moieties of the molecule. These four pools represent (i) unlabeled chlorophyll (12Por12Phy), (ii) 13C-labeled chlorophyll (13Por13Phy), and (iii, iv) chlorophyll, in which either the porphyrin or the phytol moiety was 13C-labeled, whereas the other constituent of the molecule remained unlabeled (13Por12Phy and 12Por13Phy). The kinetics of 12Por12Phy disappearance, presumably due to chlorophyll de-esterification, and of 13Por12Phy, 12Por13Phy, and 13Por13Phy accumulation due to chlorophyll synthesis provided evidence for continuous chlorophyll turnover in Synechocystis cells. The loss of 12Por12Phy was three-fold faster in a photosystem I-less strain than in a photosystem II-less strain and was accelerated in wild-type cells upon exposure to strong light. These data suggest that most chlorophyll appears to be de-esterified in Synechocystis upon dissociation and repair of damaged photosystem II. A substantial part of chlorophyllide and phytol released upon the de-esterification of chlorophyll can be recycled for the biosynthesis of new chlorophyll molecules contributing to the formation of 13Por12Phy and 12Por13Phy chlorophyll pools. The phytol kinase, Slr1652, plays a significant but not absolutely critical role in this recycling process.
通过在含有¹³C标记葡萄糖或含¹⁵N盐的条件下培养细胞，分析了集胞藻6803（Synechocystis sp. PCC 6803）中叶绿素的合成与降解。对在¹³C - 葡萄糖存在下培养不同时间段的细胞中分离出的叶绿素进行质谱分析时，检测到四个叶绿素库，它们在卟啉（Por）和叶绿醇（Phy）部分掺入的¹³C量上有显著差异。这四个库分别代表：（i）未标记的叶绿素（¹²Por¹²Phy），（ii）¹³C标记的叶绿素（¹³Por¹³Phy），以及（iii、iv）卟啉或叶绿醇部分为¹³C标记而分子的另一组成部分仍未标记的叶绿素（¹³Por¹²Phy和¹²Por¹³Phy）。¹²Por¹²Phy消失的动力学（可能由于叶绿素脱酯作用）以及¹³Por¹²Phy、¹²Por¹³Phy和¹³Por¹³Phy积累的动力学（由于叶绿素合成）为集胞藻细胞中叶绿素的持续周转提供了证据。在缺乏光系统I的菌株中，¹²Por¹²Phy的损失速度比缺乏光系统II的菌株快三倍，并且在野生型细胞暴露于强光时会加速。这些数据表明，在集胞藻中，大多数叶绿素似乎在受损光系统II解离和修复时发生脱酯作用。叶绿素脱酯作用释放的叶绿素酸酯和叶绿醇的很大一部分可被循环用于新叶绿素分子的生物合成，从而有助于形成¹³Por¹²Phy和¹²Por¹³Phy叶绿素库。叶绿醇激酶Slr1652在这个循环过程中发挥了重要但并非绝对关键的作用。
