Saeki K, Suetsugu Y, Tokuda K, Miyatake Y, Young D A, Marrs B L, Matsubara H
Department of Biology, Faculty of Science, Osaka University, Japan.
J Biol Chem. 1991 Jul 15;266(20):12889-95.
Rhodobacter capsulatus has been known to possess two ferredoxins (I and II) with distinct physicochemical and structural properties: ferredoxin I is a 2[4Fe-4S] type and the other is a [3Fe-4S] [4Fe-4S] type. To analyze their possible functional differences, their genes (fdxN and fdxA) were cloned, sequenced, and subjected to interposon mutagenesis experiments. The former gene was adjacent to a gene encoding a chloroplast-type [2Fe-2S] ferredoxin (fdxC). Mutants with inactivated fdxN and/or fdxC were obtained, and they showed virtually no growth under nitrogen-fixing conditions. Complementation experiments confirmed that both fdxN and fdxC were required for nitrogen fixation. On the other hand, we have not been able to disrupt fdxA under the screening conditions surveyed, including conditions that do not require nitrogenase activity for growth, suggesting that ferredoxin II could have an unknown essential role(s). These indicate functional differences among multiple ferredoxins in one bacterium other than in cyanobacterial heterocysts and indispensability of certain ferredoxins in nitrogen fixation other than Rhizobium meliloti FdxN.
人们已知荚膜红细菌拥有两种具有不同物理化学和结构特性的铁氧化还原蛋白（I和II）：铁氧化还原蛋白I是2[4Fe-4S]型，另一种是[3Fe-4S][4Fe-4S]型。为了分析它们可能存在的功能差异，克隆、测序了它们的基因（fdxN和fdxA），并进行了转座子诱变实验。前一个基因与编码叶绿体型[2Fe-2S]铁氧化还原蛋白（fdxC）的基因相邻。获得了fdxN和/或fdxC失活的突变体，它们在固氮条件下几乎不生长。互补实验证实fdxN和fdxC都是固氮所必需的。另一方面，在所研究的筛选条件下，包括不需要固氮酶活性来生长的条件下，我们都无法破坏fdxA，这表明铁氧化还原蛋白II可能具有未知的重要作用。这些结果表明，除了蓝藻异形胞之外，一种细菌中的多种铁氧化还原蛋白存在功能差异，并且除了苜蓿根瘤菌FdxN之外，某些铁氧化还原蛋白在固氮中不可或缺。
