Mizoguchi Tadashi, Isaji Megumi, Harada Jiro, Tamiaki Hitoshi
Department of Bioscience and Biotechnology, Faculty of Science and Engineering, Ritsumeikan University, Kusatsu, Shiga 525-8577, Japan.
Biochim Biophys Acta. 2012 Mar;1817(3):395-400. doi: 10.1016/j.bbabio.2011.12.001. Epub 2011 Dec 13.
The reaction centers (RCs) from several species of a purple photosynthetic bacterium, Rhodopseudomonas palustris, were first isolated by ammonium-sulfate fractionation of the isolated core complexes, and were successfully purified by anion-exchange and gel-filtration chromatography as well as sucrose-density gradient centrifugation. The RCs were characterized by spectroscopic and biochemical analyses, indicating that they were sufficiently pure and had conserved their redox activity. The pigment composition of the purified RCs was carefully analyzed by LCMS. Significant accumulation of both bacteriochlorophyll(BChl)-a and bacteriopheophytin(BPhe)-a esterified with various isoprenoid alcohols in the 17-propionate groups was shown in RCs for the first time. Moreover, a drastic decrease in BPhe-a with the most dehydrogenated and rigid geranylgeranyl(GG) ester was observed, indicating that BPhe-a in RC preferably took partially hydrogenated and flexible ester groups, i.e. dihydro-GG and tetrahydro-GG in addition to phytyl. Based on the reported X-ray crystal structures of purple bacterial RCs, the meaning of flexibility of the ester groups in BChl-a and BPhe-a as the cofactors of RCs is proposed.
通过对分离出的核心复合物进行硫酸铵分级分离，首次从几种紫色光合细菌沼泽红假单胞菌中分离出反应中心（RCs），并通过阴离子交换、凝胶过滤色谱以及蔗糖密度梯度离心成功纯化。通过光谱和生化分析对RCs进行了表征，表明它们纯度足够且保留了氧化还原活性。通过液相色谱 - 质谱联用（LCMS）仔细分析了纯化后的RCs的色素组成。首次在RCs中发现，细菌叶绿素（BChl）-a和细菌脱镁叶绿素（BPhe）-a与各种类异戊二烯醇在17 - 丙酸基团中酯化后有显著积累。此外，观察到具有最多脱氢和刚性的香叶基香叶基（GG）酯的BPhe - a急剧减少，这表明RC中的BPhe - a优选带有部分氢化和柔性的酯基，即除了植基之外的二氢 - GG和四氢 - GG。基于已报道的紫色细菌RCs的X射线晶体结构，提出了BChl - a和BPhe - a中酯基作为RCs辅因子的灵活性的意义。
