Suzuki J Y, Bauer C E
Department of Biology, Indiana University, Bloomington 47405.
J Biol Chem. 1995 Feb 24;270(8):3732-40.
In land plants in particular, it has been well established that chlorophyll intermediates, Mg-protoporphyrin, Mg-protoporphyrin monomethylester, protochlorophyllide, and chlorophyllide occur as monovinyl and divinyl forms. The pool of monovinyl and divinyl intermediates differ according to species, age of tissue, and light regime. In this study, we investigated the monovinyl and divinyl characteristics of protochlorophyllide and chlorophyllide in the purple non-sulfur photosynthetic eubacterium Rhodobacter capsulatus. Our results indicate that mutations in genes known to completely block the reduction of protochlorophyllide to chlorophyllide (such as bchN, bchB, and bchL mutants), accumulate a pool of monovinyl and divinyl forms of protochlorophyllide just as observed in plants. However, we also observed that directed insertion and deletion mutations in bchJ, a gene located in the photosynthesis gene cluster, affected the ratio of monovinyl and divinyl protochlorophyllide. Specifically, bchJ-disrupted strains accumulate reduced levels of bacteriochlorophyll concomitant with the accumulation of divinyl protochlorophyllide. Mutants of bchJ in combination with a second mutation in bchL still produce a mixed pool of monovinyl and divinyl protochlorophyllide; however, the ratio of monovinyl to divinyl protochlorophyllide is skewed in favor of divinyl protochlorophyllide. These results thus identify bchJ as the first sequenced gene that affects the divinyl to monovinyl ratio of photopigment intermediates in any photosynthetic organism. In addition, the results of our study also suggest that light-independent protochlorophyllide reductase is discriminatory for a monovinyl substrate.
尤其是在陆生植物中，叶绿素中间体、镁原卟啉、镁原卟啉单甲酯、原叶绿素酸酯和叶绿素酸酯以单乙烯基和二乙烯基形式存在，这一点已得到充分证实。单乙烯基和二乙烯基中间体的库因物种、组织年龄和光照条件而异。在本研究中，我们调查了紫色非硫光合真细菌荚膜红细菌中原叶绿素酸酯和叶绿素酸酯的单乙烯基和二乙烯基特性。我们的结果表明，已知完全阻断原叶绿素酸酯还原为叶绿素酸酯的基因突变（如bchN、bchB和bchL突变体），会积累单乙烯基和二乙烯基形式的原叶绿素酸酯库，正如在植物中观察到的那样。然而，我们还观察到，位于光合作用基因簇中的bchJ基因的定向插入和缺失突变影响了单乙烯基和二乙烯基原叶绿素酸酯的比例。具体而言，bchJ基因破坏的菌株积累的细菌叶绿素水平降低，同时伴有二乙烯基原叶绿素酸酯的积累。bchJ突变体与bchL中的第二个突变相结合，仍会产生单乙烯基和二乙烯基原叶绿素酸酯的混合库；然而，单乙烯基与二乙烯基原叶绿素酸酯的比例偏向于二乙烯基原叶绿素酸酯。因此，这些结果确定bchJ是第一个被测序的影响任何光合生物中光色素中间体二乙烯基与单乙烯基比例的基因。此外，我们的研究结果还表明，不依赖光的原叶绿素酸酯还原酶对单乙烯基底物具有选择性。
