MOLECULAR-GENETIC ANALYSIS OF TERMINAL STEPS IN BACTERIOCHLOROPHYLL A BIOSYNTHESIS - CHARACTERIZATION OF A RHODOBACTER-CAPSULATUS STRAIN THAT SYNTHESIZES GERANYLGERANIOL-ESTERIFIED BACTERIOCHLOROPHYLL A
MOLECULAR-GENETIC ANALYSIS OF TERMINAL STEPS IN BACTERIOCHLOROPHYLL A BIOSYNTHESIS - CHARACTERIZATION OF A RHODOBACTER-CAPSULATUS STRAIN THAT SYNTHESIZES GERANYLGERANIOL-ESTERIFIED BACTERIOCHLOROPHYLL A
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DOI：
10.1021/bi00209a006
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发表时间：
1994-11-01
期刊：
影响因子：
2.9
通讯作者：
BAUER, CE
中科院分区：
文献类型：
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作者：
BOLLIVAR, DW;WANG, SJ;BAUER, CE
对胶囊红杆菌光合作用基因簇进行了定点突变分析，以确定与细菌叶绿素a生物合成相关的遗传位点。Orf304中的一个突变体被证明在没有酯化醇存在的情况下积累了具有细菌叶绿素a环结构的四吡咯中间体细菌叶绿素a。Orf391中的一个突变体被证明合成了与香叶醇而不是正常植物酚酯化的细菌叶绿素a。后者的结果首次从遗传学上证实了细菌叶绿素a的酯化反应最初涉及香叶基香叶醇的加成，然后香叶基香叶醇部分依次还原为植醇，后者是该途径的最终产物。一株合成香叶醇酯化细菌叶绿素的胶囊假单胞菌表现出严重的光合作用生长能力受损。尽管我们观察到香叶基香叶醇酯化细菌叶绿素的合成不影响从捕光到反应中心络合物的能量转移速率，也不影响电子转移函数，电子转移函数由电子转移到初级和次级对苯二酚的产率、对苯二酚的电荷重组率和细胞色素ct的氧化速率来衡量。我们的结论是，观察到合成香叶基香叶醇的细菌叶绿素的胶囊红假单胞菌的光合作用生长速率的下降主要是由于光系统的稳态水平降低的结果。
Site-directed mutational analysis of the Rhodobacter capsulatus photosynthesis gene cluster was undertaken in order to identify and characterize genetic loci involved in bacteriochlorophyll a biosynthesis. A mutant in orf304 was shown to accumulate the tetrapyrrole intermediate ''bacteriochlorophyllide a'' which is a tetrapyrrole that has a bacteriochlorophyll a ring structure without the presence of an esterifying alcohol. A mutant in orf391 is shown to synthesize bacteriochlorophyll a that is esterified with geranylgeraniol rather than the normal phytol. This latter result provides the first genetic confirmation that esterification of bacteriochlorophyllide a initially involves the addition of a geranylgeraniol group followed by sequential reduction of the geranyl geraniol moiety to phytol which is the end product of the pathway. An R. capsulatus strain synthesizing geranylgeramiol-esterified bacteriochlorophyll is shown to exhibit severely impaired photosynthetic growth capability. This is despite our observation that synthesis of geranylgeraniol-esterified bacteriochlorophyll does not affect the energy transfer rate from light harvesting to reaction center complexes nor the electron transfer function as measured by the yield of electron transfer to the primary and secondary quinones, the charge recombination rate from the quinones, and the rate of cytochrome ct oxidation. We conclude that the observed reduction of the photosynthetic growth rate observed for R. capsulatus strains that synthesize geranylgeraniol-estefified bacteriochlorophyll is primarily a consequence of the reduced steady-state level of the photosystem.