Glutamine synthetase GS is a key enzyme in nitrogen metabolism, playing a crucial role in the assimilation of ammonia. Ammonia is a toxic compound that needs to be converted into a less toxic form for its utilization in various biological processes, such as the synthesis of amino acids, nucleotides, and other nitrogen-containing biomolecules. Glutamine synthetase catalyzes the ATP-dependent condensation of ammonia with glutamate to form glutamine, which is a less toxic and more stable form of nitrogen storage and transport.The detailed mechanism for the reaction catalyzed by glutamine synthetase is as follows:1. Activation of glutamate: The enzyme binds to glutamate and ATP, and a phosphate group is transferred from ATP to the carboxyl group of glutamate, forming an intermediate called -glutamyl phosphate and releasing ADP. This step activates the carboxyl group of glutamate for the subsequent nucleophilic attack by ammonia.2. Ammonia binding: Ammonia, which is present in the cellular environment, binds to the active site of the enzyme.3. Nucleophilic attack: The ammonia molecule acts as a nucleophile and attacks the activated -glutamyl phosphate, displacing the phosphate group and forming a new amide bond between the nitrogen atom of ammonia and the -carboxyl group of glutamate.4. Release of products: The newly formed glutamine molecule is released from the enzyme, along with inorganic phosphate Pi . The enzyme is now ready to bind to another glutamate and ATP molecule to start a new catalytic cycle.In summary, glutamine synthetase plays a vital role in nitrogen metabolism by assimilating ammonia into glutamine, which can be further utilized in various biosynthetic pathways. The enzyme catalyzes a two-step reaction involving the activation of glutamate by ATP and the subsequent nucleophilic attack by ammonia, resulting in the formation of glutamine and the release of inorganic phosphate.