Sakuragi Y, Frigaard N, Shimada K, Matsuura K
Department of Biology, Tokyo Metropolitan University, Minamiosawa 1-1, Hachioji, Tokyo, Japan.
Biochim Biophys Acta. 1999 Nov 10;1413(3):172-80. doi: 10.1016/s0005-2728(99)00092-4.
The protein assumed to be associated with bacteriochlorophyll (BChl) a in chlorosomes from the photosynthetic green filamentous bacterium Chloroflexus aurantiacus was investigated by alkaline treatment, proteolytic digestion and a new treatment using 1-hexanol, sodium cholate and Triton X-100. Upon alkaline treatment, only the 5.7 kDa CsmA protein was removed from the chlorosomes among six proteins detected by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) analysis, concomitantly with the disappearance of BChl a absorption at 795 nm. Trypsin treatment removed two proteins with molecular masses of 11 and 18 kDa (CsmN and CmsM), whereas the spectral properties of BChl a and BChl c were not changed. By the new hexanol-detergent (HD) treatment, most BChl c and all of the detected proteins except CsmA were removed from the chlorosomes without changing the BChl a spectral properties. Subsequent proteinase K treatment of these HD-treated chlorosomes caused digestion of CsmA and a simultaneous decrease of the BChl a absorption band. Based on these results, we suggest that CsmA is associated with BChl a in the chlorosomes. This suggestion was supported by the measured stoichiometric ratio of BChl a to CsmA in isolated chlorosomes, which was estimated to be between 1.2 and 2.7 by amino acid analysis of the SDS-PAGE-resolved protein bands.
对光合绿丝状细菌嗜热栖热菌的叶绿体中假定与细菌叶绿素（BChl）a相关的蛋白质进行了研究，采用了碱性处理、蛋白酶消化以及一种使用1-己醇、胆酸钠和Triton X-100的新处理方法。经过碱性处理后，在十二烷基硫酸钠聚丙烯酰胺凝胶电泳（SDS-PAGE）分析检测到的六种蛋白质中，只有5.7 kDa的CsmA蛋白从叶绿体中被去除，同时795 nm处的BChl a吸收消失。胰蛋白酶处理去除了两种分子量分别为11 kDa和18 kDa的蛋白质（CsmN和CmsM），而BChl a和BChl c的光谱特性没有改变。通过新的己醇-去污剂（HD）处理，大多数BChl c和除CsmA之外所有检测到的蛋白质都从叶绿体中被去除，而BChl a的光谱特性未改变。随后对这些经HD处理的叶绿体进行蛋白酶K处理，导致CsmA被消化，同时BChl a吸收带下降。基于这些结果，我们认为CsmA在叶绿体中与BChl a相关。通过对SDS-PAGE分离的蛋白条带进行氨基酸分析，估计分离的叶绿体中BChl a与CsmA的化学计量比在1.2至2.7之间，这一结果支持了该观点。
