Mechanism of biological nitrogen fixation

Abstract

As detd. by microrespiration and macro total N2 rate expts. in the presence of various diluent gases, the pN2 function of 2 spp. of Azotobacter is completely independent of the rate of fixation when the pN2 exceeds 0.2 atm.: below this value the rate of fixation slowly decreases. In presence of H2 the decrease begins at about pN2 0.5 atm. and proceeds rapidly with increasing pH2 so that fixation is barely detectable at pN2 0.05 atm. This inhibitory action of H2 is reversible and competitive but is not observed with cultures furnished NH4NO3; hence the effect is specific for the N-fixation process. The physicochemical properties of the N2-fixing system in Azotobacter are similar to those established for red clover plants inoculated with their specific nodule bacteria. The responsible enzyme systems in these free-living and symbiotic Ns-fixing agents are identical.