Biological nitrogen fixation is the process by which certain prokaryotes convert atmospheric nitrogen (N2) into ammonia. Nitrogen fixation often occurs within bacteria in symbiotic association with plants. The nitrogen cycle includes nitrogen fixation, the transformations by other nitrate, and the conversion of nitrate back into N2 through degradation of organic matter by fungi or other bacteria.

Read for comprehension: The process of nitrogen fixation begins as N2 is bound to the nitrogenase enzyme complex, the only family of enzymes known to accomplish this process. Metalo-enzymes are important components of the nitrogenase complex, supplying reducing power. The process begins as ferredoxin is reduced by electrons generated by photosynthesis, glycolysis or fermentation. Then, MoFe protein is reduced by ferredoxin. MoFe then binds ATP and reduces an iron-sulfur-molybdenum containing cofactor, which subsequently donates electrons to N2, producing HN=NH. Two further reductive cycles are required to reduce N2 all the way to 2NH3.