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Supramolecular Assemblies of Chlorosomes for Green Sulfur Photosynthetic Bacteria. Significance of Homologs of Bacteriochlorophylls.

绿硫光合细菌叶体的超分子组装。

基本信息

批准号：
08836011
负责人：
UEHARA Kaku
金额：
$ 1.41万
依托单位：
Osaka Prefecture University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (C)
财政年份：
1996
资助国家：
日本
起止时间：
1996 至 1997
项目状态：
已结题

项目摘要

The aggregation behavior of two homologs of bacteriochlorophyll c (BChl c) in a solvent mixture was investigated in terms of the effect of pH and a salt, and the corresponding structure was analyzed by FT-IR spectroscopy. R-[P, E] BChl c_F (R-form of BChl c with a propyl group at the C-8 position and an ethyl group at the C-12 position) and R-[E, E] BChl c_F (R-form of BChl c with two ethyl groups at positions C-8 and C-12) were isolated from the green sulfur bacterium Chlorobium limicola f.thiosulfatophilum. Each homologs showed a pH-dependent shift of the absorption maximum ; at low pH, the peak moved to the red. This tendency was also revealed by the CD spectra. The red-shift of the peaks was also induced by a high concentration of salt (NaCl) or buffer for both homologs, but only R-[E, E] BChl c_F was sensitive to the changes in solvent property. The FT-IR spectrum indicates that under the low pH condition, both homologs formed a common rather amorphous structure. On the other hand … More , a regular structure of R-[P, El BChl c_F was indicated in a solvent -water mixture, which was stabilized by a triangular interaction among three pigment molecules through the Mg ・・・OH (3^1) ・・・O=C (13^1) linkage. This structure was not found for R-[E, E] BChl c_F. These results indicate that the replacement of the side chain at the C-8 position on the macrocycle induced a different aggregation behavior. A possible heterogeneity of the in vivo rod structure of chlorosomes in green sulfur bacteria was discussed based on the above results. We found that the growth condition under limited potassium source ([K^+] = 0.2mM) was effective to enrich the BChl d homologs coexisting with a set of BChl c in chlorosomes of green sulfur bacteria Cb.limicola. As major BChl d homologs, [E, E]- and [P, E] BChl d_F were isolated and identified by ^1H-NMR signal of BChls and by Soret and Qy bands at 425nm and 650nm, respectively, which were blue-shifted than those of BChl c. The reversed phase HPLC elution profiles indicate the same proportionality for the set of four homologs ([E, M]-, [E, E]-, [P, E]- and [I, E]-) between BChl c and BChl d. The concentration of Na^+, Mg^<2+>, Ca^<2+> and Fe^<2+> influenced only to the growth of living cells, but did not onto the conversion of BChl d to BChl c. It was suggested that growth condition under limitation of potassium amount depresses the biosynthesis from BChl d to BChl c in chlorosomes. Less

研究了细菌叶绿素c（BChlc）的两种同系物在混合溶剂中的聚集行为，考察了pH和盐对BChlc聚集行为的影响，并通过红外光谱分析了BChlc的结构.从绿色硫细菌Chlorobium limicola f. thiosulfatophilum中分离得到R-[P，E] BChl c_F（BChl c的R型，C-8位有一个丙基，C-12位有一个乙基）和R-[E，E] BChl c_F（BChl c的R型，C-8和C-12位有两个乙基）。每种同系物的最大吸收峰均随pH值的变化而变化，在低pH值时，峰向红色移动。CD谱也揭示了这一趋势。高浓度的盐（NaCl）或缓冲液也能使两种同系物的峰位发生红移，但只有R-[E，E] BChlc_F对溶剂性质的变化敏感。红外光谱表明，在低pH条件下，这两种同系物形成了一个共同的，而非晶态结构。另一方面 ...更多信息在溶剂-水混合物中，通过Mg ···OH（3^1）···O=C（13^1）键，三个色素分子之间的三角形相互作用稳定了R-[P，El BChlc_F]的规则结构。在R-[E，E] BChlc_F中没有发现这种结构。这些结果表明，大环C-8位侧链的替换诱导了不同的聚集行为。根据上述结果，讨论了绿色硫细菌体内叶绿体杆状结构的可能异质性。我们发现在限制钾源（[K^+] = 0.2mM）的生长条件下，可以有效地富集绿色硫细菌Cb. limicola的叶绿素体中与一组BChl c共存的BChl d同系物。作为主要的BChl d同系物，[E，E]-和[P，E] BChl d_F被分离出来，并通过BChl s的~ 1H-NMR信号和Soret和Qy谱带分别在425 nm和650 nm处进行了鉴定，这两个谱带比BChl c的谱带蓝移。反相HPLC洗脱曲线表明BChl c和BChl d之间的四种同系物（[E，M]-、[E，E]-、[P，E]-和[I，E]-）的组具有相同的比例。Na^+、Mg^<2+>、Ca^<2+>和Fe^<2+>的浓度仅影响活细胞的生长，而不影响BChl d向BChl c的转化。这表明，钾限制条件下的生长抑制了叶绿体中BChl d向BChl c的生物合成。少