Hill S, Kavanagh E P
Nitrogen Fixation Laboratory, University of Sussex, Brighton, UK.
Microbiology (Reading). 1994 Aug;140 ( Pt 8):1917-25. doi: 10.1099/13500872-140-8-1917.
An investigation into the influence of N2 on the expression of Klebsiella pneumoniae nitrogenase has led to a reassessment of the role of the nitrogenase MoFe protein in autoregulation. Anaerobic derepression of nitrogenase (C2H2-reducing) activity, of NifD and K polypeptides, and of nifH-lac expression, following the removal of excess NH+4, were greater under N2 than Ar. This enhancement occurred in Nif+ but not in Nif- strains, and in Nif+ strains was prevented by C2H2, an inhibitor of N2 fixation. Thus N2 fixation is important for maintaining derepression. Derepression of nifH-lac under Ar in various Nif+ and Nif- strains (including NifH-, NifD-, NifB- and NifL- mutants) and of wild-type lac under N2 or Ar in a Nif+ strain were measured to investigate the regulation. The mechanism regulating the enhancement under N2 neither involved the MoFe protein of nitrogenase, as proposed by Dixon et al. (1980, Nature 286, 128-132), nor the nifL product, but was probably due to a general upgrading of the N status. Moreover, during batch growth limited by a non-repressing fixed N source, the levels of nifH-lac expression in the Nif+ and Nif- strains suggested that the nifH gene product (or Fe protein) may have a positive autoregulatory function.
对N₂对肺炎克雷伯菌固氮酶表达的影响进行的一项研究，导致了对固氮酶钼铁蛋白在自动调节中作用的重新评估。在去除过量的NH₄⁺后，N₂环境下固氮酶（乙炔还原）活性、NifD和K多肽以及nifH-lac表达的厌氧去阻遏作用比氩气环境下更强。这种增强作用发生在固氮阳性（Nif⁺）菌株而非固氮阴性（Nif⁻）菌株中，并且在Nif⁺菌株中，乙炔（一种固氮抑制剂）可阻止这种增强作用。因此，固氮作用对于维持去阻遏很重要。为了研究调节机制，测定了不同Nif⁺和Nif⁻菌株（包括NifH⁻、NifD⁻、NifB⁻和NifL⁻突变体）在氩气环境下nifH-lac的去阻遏情况，以及Nif⁺菌株在N₂或氩气环境下野生型lac的去阻遏情况。N₂环境下调节增强作用的机制既不涉及Dixon等人（1980年，《自然》286卷，128 - 132页）提出的固氮酶钼铁蛋白，也不涉及nifL产物，而可能是由于氮状态的普遍提升。此外，在由非抑制性固定氮源限制的分批培养过程中，Nif⁺和Nif⁻菌株中nifH-lac表达水平表明，nifH基因产物（或铁蛋白）可能具有正自动调节功能。
