Nitrogenase. VI. Acetylene reduction assay: Dependence of nitrogen fixation estimates on component ratio and acetylene concentration.
Acetylene reduction, an assay for nitrogenase activity (nitrogen:(acceptor) oxidoreductase, EC 1.7.99.2), Is dependent on the ratio of the two protein components of nitrogenase as well as on C2H2 concentration. As the component I : component II ratio (based on activity) is increased, the C2H2 reduction : N2 fixation ratio decreases to a minimum of 3.4 and then increases. The minimum is found at a ratio near 1 : 1. At a component I : component II ratio of 20 : 1, the C2H2 reduction : N2 fixation ratio is 5.3. Acetylene exhibits substrate inhibition in assays for nitrogenase activity. Both the apparent Km and Ki for acetylene vary as a function of the relative concentrations of components I and II present in the assay. When the more labile component II is limiting in the assay and "saturating" levels of C2H2 (above 0.1 atm) are used, N2-fixation capacity may be greatly under-estimated.
D000114:Acetylene; D000818:Animals; D001395:Azotobacter / Q000201:enzymology; D002642:Chick Embryo; D004285:Dogs; D007700:Kinetics; D008722:Methods; D009586:Nitrogen Fixation; D009591:Nitrogenase / Q000378:metabolism*; D010084:Oxidation-Reduction; D013997:Time Factors
D009591:Nitrogenase; D000114:Acetylene