Fate of Ammonia MCQ - Practice Questions with Answers

• The ammonia produced by nitrogenase is immediately protonated to form ammonium ion (NH4+). 
• As NH4+ is toxic to plants, it is rapidly used near the site of generation to synthesize amino acids.
• Amino acids synthesis takes place by three methods: reductive animation, catalytic amination and transamination.

(i) Reductive amination:

• In this process, glutamate dehydrogenase (GDH) catalyzes the synthesis of glutamic acid.

(ii) Catalytic amidation:

• It is a two step process catalyzed by glutamine synthetase (GS) and glutamate synthetase (glutamine – 2-oxoglutarate aminotransferase, or GOGAT).
• Out of the two glutamates produced one returns to GS while the other is exported to the plant.

(iii) Transamination:

• Glutamate or glutamic acid is the main amino acid from which other amino acids are derived through transamination.
• The enzyme aminotransferases (= transaminases) catalyze all such reactions.
• Transamination involves transfer of an amino group from one amino acid to the keto group of keto acid.