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首页> 外文期刊>Biochemistry >STABLE PHOTOBLEACHING OF P840 IN CHLOROBIUM REACTION CENTER PREPARATIONS - PRESENCE OF THE 42-KDA BACTERIOCHLOROPHYLL ALPHA PROTEIN AND A 17-KDA POLYPEPTIDE
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STABLE PHOTOBLEACHING OF P840 IN CHLOROBIUM REACTION CENTER PREPARATIONS - PRESENCE OF THE 42-KDA BACTERIOCHLOROPHYLL ALPHA PROTEIN AND A 17-KDA POLYPEPTIDE

机译：氯反应中心制备中P840的稳定光解-42-KDA细菌叶绿素α蛋白和17-KDA多肽的存在

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摘要

Simple procedures for the anaerobic preparation of photoactive and stable P840 reaction centers from Chlorobium tepidum and Chlorobium limicola in good yield are presented and quantitated. The subunit composition was tested by cosedimentation in sucrose density gradients. For C. limicola, it minimally comprises four subunits: the P840 reaction center protein PscA, the BChla antenna protein FMO, the FeS protein PscB with centers A and B, and a positively charged 17-kDa protein denoted PscD, The preparation from Chlorobium tepidum additionally contained PscC, a cytochrome c-551. The BChla absorption peak of the purified complexes was at 810 nm, with a shoulder at 835 nm. The ratio of the shoulder to the peak was 0.25, which corresponds to 1 reaction center per 70 BChla molecules if a uniform extinction coefficient of BChla is assumed. However, bleaching at 610 nm in continuous light corresponded up to 1 photoactive reaction center per 50 BChla molecules. Therefore, either the extinction coefficient of BChla in the reaction center is overestimated or the one for photobleaching is underestimated. In any case, the major portion of the reaction center was photoactive in the preparations. A P840 reaction center subcomplex, lacking PscD and deficient in FMO and PscB, but retaining the cytochrome c subunit, was obtained as a side product. It was photoinactive and had an absorption peak at 814 nm and a 835/814 absorbance ratio of 0.42. FMO and PscB show the tendency to form a complementary subcomplex. FMO and PscD are apparently required to stabilize the photoactive reaction center, while the cytochrome c subunit is not. [References: 49]
机译：提出并定量了从厌氧绿僵菌和细鳞绿藻厌氧制备光活性和稳定的P840反应中心的简单程序，并进行了定量。通过在蔗糖密度梯度中的沉降法测试亚基组成。对于微小隐孢子虫，它最少包含四个亚基：P840反应中心蛋白PscA，BChla触角蛋白FMO，具有中心A和B的FeS蛋白PscB以及表示为PscD的带正电荷的17-kDa蛋白。还包含PscC，一种细胞色素c-551。纯化的复合物的BChla吸收峰在810 nm，肩峰在835 nm。如果假定BChla的消光系数均匀，则肩峰与峰之比为0.25，对应于每70 BChla分子1个反应中心。但是，在连续光下610 nm处的漂白对应于每50个BChla分子最多1个光敏反应中心。因此，要么高估了反应中心中BChla的消光系数，要么低估了用于光漂白的消光系数。无论如何，反应中心的大部分在制剂中是光活性的。作为副产物，获得了缺乏PscD并且缺乏FMO和PscB但保留细胞色素c亚基的P840反应中心亚复合物。它是光惰性的，在814 nm处有一个吸收峰，其835/814吸收比为0.42。 FMO和PscB显示出形成互补亚复合物的趋势。显然需要FMO和PscD来稳定光敏反应中心，而不需要细胞色素C亚基。 [参考：49]

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