This document discusses ammonia assimilation and transamination in plants. It describes two pathways for ammonia assimilation - the primary pathway involving glutamine synthetase and glutamate synthase, and the alternative pathway using glutamate dehydrogenase. The primary pathway converts ammonia into amino acids using glutamine synthetase to produce glutamine, which is then acted on by glutamate synthase to form two molecules of glutamate. Transamination reactions transfer amino groups between amino acids and alpha-keto acids using transaminases and pyridoxal phosphate as a cofactor. Transamination is important for forming non-essential amino acids and recycling carbon skeletons.

1. Ammonia Assimilation and
Transamination
CHARU SHARMA
BOTANY (H) 3rd YEAR

3. Ammonia Assimilation
 Conversion of ammonia generated
from nitrate assimilation or
photorespiration into amino acid.
 2 pathways – i. Primary Pathway
ii. Alternative Pathway

4. Primary Pathway
2 enzymes involved :
a) Glutamine synthetase (GS) –
Available in two forms- in cytosol , and roo
plastid/shoot chloroplast
a) Glutamate synthase (also known as
GOGAT)
GOGAT – Glutamine 2-oxo-glutarate
aminotransferase

5. Glutamine synthetase action
Cytosolic form –
 Expressed in germinating
seeds or in vascular
bundle of roots and shoots.
 Produce glutamine for
intracellular nitrogen transport.
Root plastid/Shoot
chloroplast form –
 In roots, it produces amide
nitrogen for local consumption.
 In shoots, it reassimilates
photorespiratory NH4
+

6. Glutamate synthase action
 Transfers amide group of glutamine to
2-oxoglutarate, and yields two
glutamate molecules.

7. Types of GOGAT
 NADH-GOGAT
 accepts electrons from NADH.
 located in plastids of non-photosynthetic tissue like roots or VB
of developing leaves.
Glutamine + 2-oxoglutarate + NADH + H+
2 Glutamate + NAD+
 Fd-GOGAT
 accepts electron from ferrodoxin.
 located in chloroplast and serves in photorespiratory nitrogen
metabolism.
Glutamine + 2-oxoglutarate + Fdred 2 Glutamate +
Fdox

8. Alternative Pathway
 The enzyme involved is Glutamate Dehydrogenase
(GDH), hence known as GDH pathway.
 Catalyzes synthesis and deamination of glutamate.
 Reversible

9. Transamination Reaction
 Transfer of amino group of an amino acid to
α-keto acid resulting in formation of new
amino acid and new keto acid.
 Catalyzed by Transaminase
(Aminotransferase)
 Co-factor: Pyridoxal phosphate(Vitamin B6)
 Reversible

10.  Not all amino acids undergo
transamination reaction.
Eg. Lysine, Threonine, Proline,
Hydroxy proline

11. Role of Pyridoxal
Phosphate(PLP)
 Serves as a carrier of amino group
 Transfer of α-amino group to PLP forms
Pyridoxamine Phosphate, and a keto acid.
 α-amino group is finally transferred to
acceptor keto acid to form a new amino acid.

12. Example:
 Catalyzed by Aspartate Transaminase
 Catalyzed by Alanine Transaminase

13. Significance
 Formation of non-essential amino
acids
Eg: Alanine , Aspartate
 Recycling of carbon skeletons.
Eg: Oxaloacetate, Pyruvate