The root nodules of leguminous plajit have a red pigment called leghaemoglobin. It is reddish pigment found in cytoplasm of host cells. Leghaemoglobin maintains steady supply o oxygen to nitrogen fixing bacteria for respiration.
The ATP generated in the process of respiration of bacteria is used for nitrogen fixation. The bacteroids contain the enzyme nitrogenase. The fret Atmospheric nitrogen is first bound to the enzyme surface and is not released until it is completely reduced to ammonia.
The nitrogenase enzyme complex is composed of two proteins (i) non-heme iron protein and (ii) iron molybdenum protein. The non-heme iron protein reacts with ATP and reduces molybdenum protein which ultimately reduces nitrogen into ammonia. At each step, pai of hydrogen are added. The hydrogen is obtained from Glucose-6-phosphate of host cells. Glucose 6 phosphates serves as reduced substrate and reduced XADP together with ferrodoxin function as electron carriers. ATP provides the energy for nitrogen fixation.
Ammonia so formed is utilised for the synthesis of aminoacids. Symbiotic forms fix more nitrogen in comparison to asymbiotic forms.
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(Where “1” stands for enzyme Glucose-6-phosphate dehydrogenase, ‘2’ for XADPH. ferrodoxin oxido reductase, ‘3’ for enzyme iron containing protein component of nitrogenase, ‘4’ for iron- molybdenum component of nitrogenase)
The reduction of X2 to Nil3 in both non-symbiotic and symbiotic forms is same except few difference such as (i) in symbiotic nitrogen fixation the electron donor is glucose-6-phosphate in stead of pyruvic acid (ii) Glucose-6-phosphate is converted into 6-phosphogluconic acid with reduction of XADP to XADPH+IL (iii) Electrons are transported to nitrogen complex from XADPH by reduction of ferrodoxin. (iv) Leghaemoglobin- oxygen carrier occurs in root nodules.