5-Aminolevulinic acid availability and control of spectral complex formation in hemA and hemT mutants of Rhodobacter sphaeroides.
5-Aminolevulinic acid availability and control of spectral complex formation in hemA and hemT mutants of Rhodobacter sphaeroides.
复制标题
球形红杆菌 hemA 和 hemT 突变体中 5-氨基乙酰丙酸的可用性和光谱复合物形成的控制。
DOI：
10.1128/jb.175.8.2304-2313.1993
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发表时间：
1993
影响因子：
3.2
通讯作者：
Kaplan,S
中科院分区：
文献类型：
--
作者：
Neidle,EL;Kaplan,S
在光合细菌球形红细菌中，两个基因hemA和hemT各自编码一种不同的5-氨基乙酰丙酸（ALA）合酶同工酶（E。L. Neidle和S. Kaplan，J. Bacteriol. 175：2292-2303，1993）。这种酶催化四吡咯形成的分支途径中的第一步和限速步骤，导致血红素、细菌叶绿素和类咕啉的生物合成。为了确定hemA和hemT的功能，构建了具有特定染色体破坏的突变株。这些染色体的破坏使得hemA和hemT能够精确地定位在两个R中较大和较小的一个上。sphaeroides染色体。携带单个hemA或hemT破坏的突变体在不添加ALA的情况下生长良好，而其中hemA和hemT均被灭活的突变体HemAT 1需要外源ALA才能生长。比较了所有菌株的生长速率、ALA合成酶水平和含细菌叶绿素的胞质膜内光谱复合物的量。在光合生长条件下，细菌叶绿素，类胡萝卜素，B800-850和B875捕光复合物的水平显着低于Hem突变体比野生型。在突变菌株中，可用的细菌叶绿素似乎优先针对B875捕光复合物相对于B800-850复合物。在HemAT 1菌株中，B800-850复合物的量随ALA浓度的变化而变化，在ALA限制条件下，B800-850复合物不能被检测到。在Hem突变体中，存在对应于编码B800-850和B875复合物的结构多肽的puc和puf操纵子的异常转录水平。这些结果表明，hemA和hemT的表达是耦合的遗传控制的R。类球孢菌光合器
In the photosynthetic bacterium Rhodobacter sphaeroides, two genes, hemA and hemT, each encode a distinct 5-aminolevulinic acid (ALA) synthase isozyme (E. L. Neidle and S. Kaplan, J. Bacteriol. 175:2292-2303, 1993). This enzyme catalyzes the first and rate-limiting step in a branched pathway for tetrapyrrole formation, leading to the biosynthesis of hemes, bacteriochlorophylls, and corrinoids. In an attempt to determine the functions of hemA and hemT, mutant strains were constructed with specific chromosomal disruptions. These chromosomal disruption allowed hemA and hemT to be precisely localized on the larger and smaller of two R. sphaeroides chromosomes, respectively. Mutants carrying a single hemA or hemT disruption grew well without the addition of ALA, whereas a mutant, HemAT1, in which hemA and hemT had both been inactivated required exogenous ALA for growth. The growth rates, ALA synthase enzyme levels, and the amounts of bacteriochlorophyll-containing intracytoplasmic membrane spectral complexes of all strains were compared. Under photosynthetic growth conditions, the levels of bacteriochlorophyll, carotenoids, and B800-850 and B875 light-harvesting complexes were significantly lower in the Hem mutants than in the wild type. In the mutant strains, available bacteriochlorophyll appeared to be preferentially targeted to the B875 light-harvesting complex relative to the B800-850 complex. In strain HemAT1, the amount of B800-850 complex varied with the concentration of ALA added to the growth medium, and under conditions of ALA limitation, no B800-850 complexes could be detected. In the Hem mutants, there were aberrant transcript levels corresponding to the puc and puf operons encoding structural polypeptides of the B800-850 and B875 complexes. These results suggest that hemA and hemT expression is coupled to the genetic control of the R. sphaeroides photosynthetic apparatus.