The 17-propionate esterifying variants of bacteriochlorophyll-a and bacteriopheophytin-a in purple photosynthetic bacteria
The 17-propionate esterifying variants of bacteriochlorophyll-a and bacteriopheophytin-a in purple photosynthetic bacteria
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紫色光合细菌中细菌叶绿素-a 和细菌脱镁叶绿素-a 的 17-丙酸酯化变体
DOI：
10.1016/j.jphotobiol.2014.12.013
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发表时间：
2015
期刊：
影响因子：
--
通讯作者：
H. Tamiaki
中科院分区：
文献类型：
--
作者：
T. Mizoguchi;M. Isaji;J. Harada;Y. Tsukatani;H. Tamiaki
大多数紫色光合细菌都含有细菌叶绿素(BCHL)-a(镁复合体)和细菌素(BPhe)-a(其游离碱)作为其光活性色素。这些色素由两部分组成：作为生色团的环状四吡咯和作为17位丙酸酯化基团的长碳氢链。在两种颜料中，碳氢链通常是异戊二烯类型的C20植基(Phy)。在BCHL-a的酯基中，在BCHL-非生物合成的最后阶段发现了香叶基(GG)、二氢香叶基(DHGG)和四氢香叶基(THGG)等几个变体。另一方面，BPhe-a中的酯化变异体还没有得到太多的研究，这是因为这种色素相对于Bchl-a的含量较低。酯化基团不影响单体状态下颜料的电子吸收性能，但显著改变了颜料的疏水性。在这项研究中，用高效液相色谱法分析了6个系统发育不同类别的紫色细菌中的Bchl-a和BPhe-in在17-丙酸残基上的酯化基团。在所研究的所有细菌种中，除通常的Phy外，还发现了BChls-a和BPhes-gG、DHGG和THGG。在一些种中，与相应的BChls-a相比，经GG、DHGG和THGG酯化的BPhes占总BPhe的比例显著下降。尤其是BPhe-a与GG的相对含量显著降低。这可能表明，BPhe-Aas作为反应中心的辅助因子，优先以部分还原的柔性链(THGG和Phy)而不是较少的还原和刚性链(GG和DHGG)酯化。
Most purple photosynthetic bacteria contain bacteriochlorophyll(BChl)-a(a magnesium complex) and bacteriopheophytin(BPhe)-a(its free base) as their photoactive pigments. These pigments are composed of two parts: a cyclic tetrapyrrole as the chromophore and a long hydrocarbon-chain as the propionate-type esterifying group at the 17-position. The hydrocarbon-chain is usually an isoprenoid-type C20phytyl (Phy) group in both the pigments. In the ester group of BChl-a, several variants such as geranylgeranyl (GG), dihydrogeranylgeranyl (DHGG) and tetrahydrogeranylgeranyl (THGG) groups were found in the final stage of BChl-abiosynthesis. On the other hand, the esterifying variants in BPhe-ahave not been studied as much due to the lower levels of this pigment relative to BChl-a. The esterifying group does not affect the electronic absorption properties of such pigments in the monomeric state, but drastically alters the hydrophobicity. In this study, BChl-aand BPhe-ain the six phylogenetically distinct classes of purple bacteria were analyzed in terms of their esterifying groups in the 17-propionate residues, using high-performance liquid chromatography. Both BChls-aand BPhes-acarrying GG, DHGG and THGG in addition to the usual Phy were found for all the bacterial species studied at measurable levels. In some of the species, the ratio of BPhes-aesterified with GG, DHGG and THGG over the total BPhe-adrastically decreased in comparison with that of the corresponding BChls-a. Especially, the relative content of BPhe-awith GG largely decreased. This observation might indicate that BPhe-aas a cofactor of reaction centers was preferentially esterified with partially reduced and flexible chains (THGG and Phy) rather than less reduced and rigid ones (GG and DHGG).