Process of progressive reduction of one molecule of nitrogen during fixation in leguminous plants:
(i) The nodules are the sites of nitrogen fixation in leguminous plants. Nodules contain leghaemoglobin (Lb) and the enzymenitrogenase.
(ii) Leghaemoglobin is a pink colour pigment similar to haemoglobin of vertebrates and functions as an oxygen-scavenger and protects the nitrogenase from oxygen.
(iii) During this process, a dinitrogen (N ≡ N) molecule is reduced by the addition of hydrogen atoms into two molecules of ammonia catalysed by the nitrogenase enzyme.
(iv) It requires :
(a) a strong reducing agent,
(b) energy in the form of ATP to transfer the hydrogen atom and
(c) the enzyme systems.
The reaction is as follows:
N2 + 8e- + 8H+ + 16 АТР → 2NH3 + H2 + 16 ADP + 16 Pi
