Biological nitrogen fixation is the process in which certain living organisms convert the free nitrogen into those compounds which can be used by plants.
(a) The organisms may be free-living bacteria (e.g., Azotobacter), symbiotic bacteria like Rhizobium or Cyanobacteria.
(b) The enzyme involved in the process is nitrogenase,
which is a Mo-Fe protein.
(c) During this process, the atmospheric nitrogen is reduced by the addition of hydrogen.
(d) The three bonds between the two nitrogen atoms (N = N) are broken and hydrogen is progressively added to from ammonia.
(e) This fixation requires three components :
(i) ATP, to supply energy.
(ii) A strong reducing agent, to transfer hydrogen atoms.
(iii) The enzyme system (nitrogenase)
(g) The overall reaction is as follows :