The first organic compounds of nitrogen assimilation are amino acids. They are synthesised by following three methods.
(1) Reductive animation : In the presence of dehydrogenase (e.g., Glutamate dehydrogenase, Aspartate dehydrogenase), a reduced coenzyme (NADH or NADPH), ammonia can directly combine with a keto organic acid like a-ketoglutaric acid and oxaloacetic acid to form amino acid, a-ketoglutaric acid + NH4+ + NAD(P)H
Lipases ^ Glutamate + H20 + NAD(P) Oxaloacetic acid + NH4+ + NAD(P)H
Chlorophyll"”* Aspartate + H20 + NAD(P)
(2) Catalytic Animation : Ammonia combines with catalytic amounts of glutamic acid in the presence of ATP and enzyme glutamine synthetase. It produces an amide called glutamine. Glutamine reacts with a-ketoglutaric acid in the presence of enzyme glutamate synthetase to form two molecules of glutamate. Reduced co-enzyme (NADH or NADPH) is required.
Glutamate + NH4+ + ATP synthetase ) Glutamine + ADP + Pi
Glutamine + a-ketoglutaric acid + NAD(P)H .
Gluramine v „
" synthetase > 2Glutamate + NAD(P)
(3) Transamination : It is transfer of amino group (>CHNH2) of one amino acid with the keto group (x = 0) of keto acid. The enzyme required is transaminase or amino transferase. Glutamine acid is the primary amino acid involved in transfer of amino group.
Glutamic + Oxaloacetic acid
a-ketoglutaric acid + Aspartic