Nitrogen fixation is the process by which atmospheric nitrogen N2 is converted into ammonia NH3 , which can then be used by plants and other organisms to synthesize amino acids, nucleic acids, and other nitrogen-containing compounds. This process is primarily carried out by certain bacteria, known as nitrogen-fixing bacteria, which can either live freely in the soil or form symbiotic relationships with plants, particularly legumes.The key enzyme responsible for nitrogen fixation is nitrogenase, which is found in nitrogen-fixing bacteria. Nitrogenase is a complex enzyme composed of two metalloproteins: the dinitrogenase reductase Fe protein and the dinitrogenase MoFe protein . The nitrogenase enzyme catalyzes the reduction of atmospheric nitrogen N2 to ammonia NH3 using ATP and electrons from a reduced electron carrier, such as ferredoxin or flavodoxin.The overall reaction for nitrogen fixation is:N2 + 8H+ + 8e- + 16ATP 2NH3 + H2 + 16ADP + 16PiIn the case of symbiotic nitrogen fixation, such as in the root nodules of leguminous plants, the bacteria e.g., Rhizobium invade the plant's root cells and form specialized structures called nodules. Within these nodules, the plant provides the bacteria with organic compounds as an energy source, while the bacteria fix nitrogen and supply the plant with ammonia.Once ammonia is produced, it can be assimilated into amino acids through two main biochemical pathways: the glutamine synthetase-glutamate synthase GS-GOGAT pathway and the glutamate dehydrogenase GDH pathway.1. GS-GOGAT pathway:This is the primary pathway for ammonia assimilation in most organisms. It involves two key enzymes: glutamine synthetase GS and glutamate synthase GOGAT .a Glutamine synthetase GS catalyzes the ATP-dependent condensation of ammonia with glutamate to form glutamine:Glutamate + NH3 + ATP Glutamine + ADP + Pib Glutamate synthase GOGAT then transfers the amide group of glutamine to 2-oxoglutarate -ketoglutarate , producing two molecules of glutamate:Glutamine + 2-oxoglutarate + NAD P H 2 Glutamate + NAD P +One of the glutamate molecules can be used to synthesize other amino acids through transamination reactions, while the other can be recycled back to glutamine in the GS reaction.2. GDH pathway:This pathway is less common and usually occurs under conditions of high ammonia concentrations. Glutamate dehydrogenase GDH catalyzes the reversible reaction between glutamate and 2-oxoglutarate, incorporating ammonia directly:2-oxoglutarate + NH3 + NAD P H Glutamate + NAD P +Once glutamate is formed, it can serve as a substrate for the synthesis of other amino acids through transamination reactions.