Gordon J K, Shah V K, Brill W J
J Bacteriol. 1981 Dec;148(3):884-8. doi: 10.1128/jb.148.3.884-888.1981.
No inhibition of nitrogenase activity by physiological levels of NH4+ or carbamyl phosphate was observed in extracts of Azotobacter vinelandii. All of the 15N2 reduced by cultures which received no NH4+ was found in the cells. By contrast, more than 95% of the 15N2 reduced by cultures which had been given NH4+ was found in the medium. Failure to examine the culture medium would lead to the erroneous conclusion that N2 fixation is inhibited by NH4+. Nitrogenase in a derepressed mutant strain of A. vinelandii was fully active in vivo in the presence of NH4+. The addition of NH4Cl to N2-fixing cultures resulted in no decrease in the N2-reducing activity of intact cells of Klebsiella pneumoniae or Clostridium pasteurianum and only a small (15%) decrease in A. vinelandii. Therefore, no significant inhibition of nitrogenase by NH4+ or metabolites derived from NH4+ exists in A. vinelandii, K. pneumoniae, or C. pasteurianum.
在棕色固氮菌提取物中未观察到生理水平的NH₄⁺或氨基甲酰磷酸对固氮酶活性有抑制作用。在未添加NH₄⁺的培养物中还原的所有¹⁵N₂都存在于细胞中。相比之下，在添加了NH₄⁺的培养物中还原的¹⁵N₂，超过95%存在于培养基中。若不检测培养基，将会得出N₂固定受NH₄⁺抑制这一错误结论。在棕色固氮菌的一个去阻遏突变株中，固氮酶在体内NH₄⁺存在的情况下仍具有完全活性。向固氮培养物中添加NH₄Cl，不会导致肺炎克雷伯菌或巴氏梭菌完整细胞的N₂还原活性降低，而在棕色固氮菌中仅导致小幅（15%）降低。因此，在棕色固氮菌、肺炎克雷伯菌或巴氏梭菌中，NH₄⁺或源自NH₄⁺的代谢物对固氮酶没有显著抑制作用。
