1. The document discusses various reactions involved in amino acid metabolism including deamination, desulfuration, transamination, and transmethylation. 2. Deamination is the removal of the amino group from an amino acid, which can occur oxidatively or non-oxidatively. Oxidative deamination uses amino acid oxidases and releases ammonia and hydrogen peroxide. 3. Transamination is the reversible transfer of the amino group between amino acids and alpha-keto acids, producing new amino acids and keto acids. It requires pyridoxal phosphate and does not release free ammonia.

1. General reactions
involved in Amino acid Metabolism
Dr. Dhiraj J Trivedi

2. Reactions of Amino acid
metabolism
1. De amination
2. Desulphuration
3. Trans amination
4. Trans methylation

3. DEAMINATION
Short note on 5marks

4. Deamination
• DEFINITION:
• Deamination is the process by which N- atom of
amino acid is removed as free NH3.
• Types: It can be of two types
• 1] Oxidative deamination.
• 2] Non-oxidative deamination.

5. 1] OXIDATIVE DEAMINATION:
• Site: Liver and Kidney
• Coenzymes: Pyridoxal phosphate
• Enzymes: D- amino acid oxidases and L - amino
acid oxidases.
• Even though D- amino acids are normally not
present in human body their concentration is
higher than L- amino acid oxidases in the body.
• L- amino acid oxidases are Flavoprotein.
• They are reoxidized at substrate level, directly
by molecular oxygen forming H2O2.

6. Step-I: The amino acid is first dehydrogenated by Flavoprotein
of L- amino acid oxidase forming α Imino acid.
Step-II Water molecule is added which, decomposes to form
Ketoacid and N is lost as NH3.
1] OXIDATIVE DEAMINATION:

7. 2] Non oxidative deamination:
• There are certain amino acids, which can be non-
oxidatively deaminated by specific enzymes.
• a] Amino acid dehydrase:

8. b] Amino acid desulphurase:
• Sulphur containing amino acid like Cysteine and
homo-Cysteine are deaminated by primary
desulphuration forming imino acid.
• It is then spontaneously hydrolyzed to α keto acid and
NH3 is made free.

9. 3] Deamination of L- Glutamic acid:
• L- Glutamic acid is not deaminated by L- amino acid oxidase
but it require L- glutamate dehydrogenase.
• Reaction: L- glutamate dehydrogenase Act on L- Glutamic
acid to form α imino glutaric acid. Which on addition of
molecule of H2O forms NH3 and α keto glutarate.
• Also called as Transdeamination, Reaction is reversible.

10. TRANS AMINATION
Short note on 5marks

11. Transamination:
• Definition:
• Transamination is a reversible reaction
• α -NH2 group of amino acid is transferred
to α- keto acid, resulting in the formation of
new amino acid and a new keto acid.
Thus at the end of reaction donor amino acid
becomes new keto acid & The recipient keto acid
becomes new amino acid .

12. Transamination:
• Transamination is a reversible reaction.
• It is only for intermolecular transfer of
NH2 group.
• In this reaction free ammonia is not
released during reaction.
• It requires Pyridoxal phosphate , as
coenzyme.

13. Salient feature of Transamination:
• Site of transamination: Principally in all cells
• major tissues Liver, Heart, Kidney and Brain.
• Enzymes: called transaminases or aminotransferases.
• Co-enzymes: Pyridoxal Phosphate (B6-P)
• Substrates: Amino acids & Keto acids
• End product : Keto acid & non essential amino
acids

14. Salient feature of Transamination:
• Substrates: Amino acids:
• Almost all amino acids undergo transfer of
amino group to small or large extent.
• Exceptions --
• Lysine , Threonine , Proline and
hydroxyrpoline
• do not take part in transamination reaction.

15. Salient feature of Transamination:
• Keto acids: There are only three keto acids,
Ketoglutarate, Pyruvate and Oxaloacetate which acts
as recipient molecules in transamination reactions.
All three are component of TCA cycle.
• Reversible reaction:
• Hence keto acid can be derived from amino acid,
and amino acids can be obtained from Ketoacid.

16. Mechanism of enzyme action:
• Requires Pyridoxal phosphate as co-enzyme.
• Reaction occur in two stages
• 1] Amino group from amino acid is accepted by
Pyridoxal phosphate to form pyridoxamine and amino
acid is converted to keto acid.
• 2] In second stage, Amino group is accepted by Keto
acid from pyridoxamine and gets converted to amino
acid. The Pyridoxal phosphate is regenerated.

17. Mechanism of enzyme action:

18. Alanine Pyruvic acid
α-Keto Glutarate Glutamate
Serum Glutamate Pyruvate Transaminase
Pyridoxal phosphate
Examples of Transamination:
Aspartate Oxalo acetate
α-Keto Glutarate Glutamate
Serum Glutamate Oxaloacetate Transaminase
Pyridoxal phosphate
1
2

19. α-Keto Glutarate
Glutamate
Pyridoxal phosphate
α-Amino
group of
Various
amino acids
α-Keto Glutarate acts as
common acceptor of α-Amino group
In transaminase reactions

20. Clinical Significance:
• Two transaminases having clinical significance
1. Serum glutamate Pyruvate transaminase is
also named as alenine transaminase (ALT).
• Normal level is 5 to 35 IU/L.
• Its activity increases in liver diseases.
2. Serum glutamate oxaloacetate transaminase is
also named as aspartate transaminase (AST).
• Its normal value is 5 to 40 IU/L.
• The increased activity is seen in heart diseases.

21. Functions of transamination:
1] Inter-conversion of amino acid to keto acid
and keto acid to amino acid. This provides
non-essential amino acids in the body.
2] Utilization of alpha keto acids when in excess.
3] Prevents toxicity of ammonia as it is not at all
released free during reaction.

22. TRANS METHYLATION
Explain the reaction of transmethylation 5 marks

23. Trans methylation
• An important biological transfer of methyl
group with in amino acids.
• Process similar to transamination.
• The difference is transfer of methyl group
instead amino group.

24. Trans methylation
• DEFINITION:
The transfer of methyl group (-CH3) from active
Methionine to an acceptor molecule is known as
Transmethylation.
• Methionine has to be activated to S- adenosyl
Methionine (SAM) to donate the methyl group.

25. Trans methylation
• All compounds having –CH3 group cannot act as
methyl group donor.
• Methyl group attached to N atom or S atom
becomes active and can become methyl group
donor.

26. Enzymes & Coenzymes
of trans methylation
• Enzymes:
• Enzymes involved are collectively known as
methyltransferases or transmethylases.
• Coenzymes: Tetra hydro folate (THF) is a coenzyme
that actively participates in methyl group transfer.
• Vit B12 is also involved in this reaction (makes folate
free).

27. Significance of Trans methylation:
1] Transmethylation is an essential process since many
biological compounds become functionally active only
after methylation.
2] Transmethylation synthesizes Biologically important
compounds like Choline, Creatine, Epinephrine, Nor-
epinephrine.

28. Significance of Trans methylation:
3] Amino acid residues of protein on methylation control
protein turn over. In fact methylation protect the
proteins from immediate degradation.
4] In plants and animals Transmethylation help to
synthesis certain hormone. ( Epinephrine, Nor
epinephrine)

29. Significance of Trans methylation:
5] Decrease of Transmethylation will affect synthesis of
choline and in turn phospholipid. This leads to
decreased formation of lipoproteins and accumulation
of lipid in liver causing fatty liver.
6] Choline synthesis is also required for the synthesis of
Acetyl- choline, a neurotransmitter.

30. IMPORTANT TRANSMETHYLATION REACTIONS:
• S-adenosyl Methionine acts as donor of methyl group.
• Transmethylation is a type of one carbon metabolic reaction.
Methyl group acceptors Methylated product
Guanido acetate Creatine
Nor-epinephrine Epinephrine
Epinephrine Metanephrine
Ethamolamine Choline
Phosphatidyl Ethamolamine Lecithin Or Phosphatidyl choline
Serine Choline
Acetyl serotonin Melatonin
Homo Cysteine Methionine

31. Q: What is transmethylation reaction? Give two examples.
• A: Transmethylation: Transfer of methyl group (-CH3) from
active Methionine to an acceptor is known as
Transmethylation reaction.
• S- Adenosyl methionine (SAM) is active methyl group
donor in many transmethylation reactions. Examples are ,
SAM
Guanidinoacetate Creatine
Serine Choline
Nor epinephrine Epinephrine
S-adenosyl
homocysteine
SAM S-adenosyl
homocysteine
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