Cyanamide: a new substrate for nitrogenase.
(1) Cyanamide (N identical to C-NH2) has been shown to be a substrate for purified Mo-nitrogenases of Klebsiella pneumoniae and Azotobacter chroococcum, with apparent Km values near 0.8 mM. (2) Reduction products were CH4, CH3NH2 and NH3 formed by pathways requiring 6 or 8 electrons: N identical to CNH2 + 6e + 6H+----CH3NH2 + NH3; N identical to CNH2 + 8e + 8H+----CH4 + 2NH3 (3) Acetylene reduction and hydrogen evolution were inhibited more than 75% by cyanamide (10 mM). Cyanamide also inhibited total electron flux at nitrogenase protein component ratios (Fe/MoFe) near 10. (4) Cyanamide was also a substrate for the recently isolated Va-nitrogenase of A. chroococcum, but with an apparent Km of 2.6 mM showed weaker binding and an 8-fold lower Vmax than did either Mo-nitrogenase. (5) The component ratios of nitrogenase proteins favouring CH4 formation was 3.5 Fe/MoFe protein and 1 Fe/VaFe protein.
Miller
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Plant Research Centre, Agriculture Canada, Ottawa.
Eady
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D000114:Acetylene / Q000037:antagonists & inhibitors; D000641:Ammonia; D003484:Cyanamide / Q000494:pharmacology*; D003486:Cyanides / Q000494:pharmacology*; D006859:Hydrogen / Q000037:antagonists & inhibitors; D007700:Kinetics; D008697:Methane; D008744:Methylamines; D008982:Molybdenum / Q000494:pharmacology; D009591:Nitrogenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D013379:Substrate Specificity; D014639:Vanadium / Q000494:pharmacology
D003486:Cyanides; D008744:Methylamines; D014639:Vanadium; D003484:Cyanamide; D000641:Ammonia; D006859:Hydrogen; D008982:Molybdenum; C027451:methylamine; D009591:Nitrogenase; D000114:Acetylene; D008697:Methane