Transamination and Deamination Reactions and MCQs for GPAT, NEET, CSIR NET, UPSC, SSC Exams

For the catabolism of amino acid, following stages are involved.

Removal of alpha-amino group in the form of ammonia by following reactions.
1. Transamination:- Catalyzed by aminotransferase or transaminase.
2. Deamination:- It may be oxidative or non oxidative
  1. Oxidative deamination:- Catalyzed by glutamate dehydrogenase or amino acid oxidase.
  2. Non-oxidative deamination:- Catalyzed by amino acid dehydratase, amino acid desulfhydrases and histidase.
Disposal of ammonia in the form of urea in liver by the reactions of urea cycle.
Catabolism of remaining carbon atoms to form CO2 and water through TCA cycle.

TRANSAMINATION

Definition:- It involves transfer of alpha-amino group from alpha-amino acid to alpha keto acid and forms new alpha-amino acid and alpha-keto acid without any loss of alpha-amino group. This reaction is catalyzed by transferase or transaminase.

Alpha-ketoglutarate is the most common acceptor of amino group.

Silent features of transamination

All types of transaminase enzyme requires pyridoxal phosphate (PLP) as co-enzyme. Eg of transaminase are: alanine transaminase (ALT) and aspartate transaminase (AST)

Alanine transaminase (ALT): Also called as glutamate pyruvate transaminase (GPT). It catalyzes the transfer of amino group of alanine to alpha-ketoglutarate which results in the formation of pyruvate and L-glutamate.

Aspartate transaminase (AST): Also called as glutamate oxaloacetate transaminase (GOT). It catalyzes the transfer of amino group of aspartate to alpha-ketoglutarate which results in the formation of oxaloacetate and L-glutamate.

2. Specific transaminase enzyme is present for specific pair of amino acid and keto acid.

3. In this reaction, no free ammonia is liberated. Perhaps only amino group is transferred

4. Transamination is reversible.

5. Transamination diverts the excess amino acid towards the energy generation process

Mechanism of Transamination

Transamination occurs in two stages:

transfer of amino group to PLP to form pyridoxamine phosphate
The amino acid of pyridoxamine phosphate is then transferred to keto acid to produce new amino acid and the enzyme and also the PLP is regenerated.

Metabolic Significance of Transamination reaction

It provides mechanism for the collection of amino group from alpha-amino acid and introduce then in alpha-ketoglutarate to form L-glutamate.
L-glutamate is the only amino acid which can be easily removed by oxidative deamination than other amino acids.
Since transamination reaction is reversible, so it can work for both catabolism and synthesis of amino acid.

Clinal significance of transamination reactions

Increased serum level of transaminase as SGPT or SGOT are important i the diagnosis of heart and liver damage.

DEAMINATION

Definition:- Removal of amino group from the amino acid as ammonia is called as deamination. Transamination is only shuffling of amino groups of amino acid; While on the other hand, deamination is liberation of ammonia for synthesis of urea.

Oxidative deamination by glutamate dehydrogenase:-

Oxidative deamination is liberation of ammonia from the amino group of amino acid together with oxidation. It occurs mostly in liver and kidney.

The alpha-amino group of most of the alpha-amino acid are transfer to the alpha-ketoglutarate to form L-glutamate. The L-glutamate then undergoes oxidative deamination by the action of L-glutamate dehydrogenase which require NAD or NADP as oxidizing agents. So the net removal of alpha-amino group to ammonia requires a combine functioning of glutamate dehydrogenase and glutamate transaminase.

Significance of Oxidative deamination by glutamate dehydrogenase

Since it is reversible, so can work for both catabolism and biosynthesis.
In normal condition, glutamate dehydrogenase is present in sufficient amount in serum, but increased activity is observed during liver diseases.

Oxidative deamination by amino acid oxidases

Both D and L-amino acid oxidases occur in the kidney and liver cell in low activity. These enzyme uses auto-oxidative FMN and FAD as co-enzyme.

The enzyme oxidizes the alpha-amino acid to less stable alpha-imino acid which on decomposition form alpha-ketoglutarate and ammonia ion. In this reaction, oxygen is reduced to hydrogen peroxide which is later decomposed to oxygen and water by catalase.

The activity of L-amino acid oxidase is much low than D-amino acid oxidase. Because the L-amino acid oxidase does not act on glycine and dicarboxylic acids. And since due to its very low activity, this enzyme has not significant role in amino acid metabolism

Non-Oxidative deamination by amino acid dehydratase

Some of the amino acid can directly deaminated to liberate ammonia without coupling with oxidation. It is divided in 3 types:

Amino acid dehydrases:- Serine and threonine amino acid contains OH group and undergo non-oxidative deamination by PLP-dependent dehydrases
Amino acid desulfhydrases:- Sulfur containing amino acids like cysteine undergo deamination together with desulfhydration to give keto acids.
Deamination of histidine:- Histidine undergo non-oxidative deamination to liberate ammonia using histidase enzyme.

Multiple choice questions (MCQs)

1. Catabolism of amino acid require how many stages?
A. 2

B. 3

C. 4

D. 5

2. Which reaction is required for the removal of alpha-amino group to form ammonia?
A. Transamination

B. Transcription

C. Deamination

D. Both A and C

3. Transamination reaction is catalyzed by which enzyme?
A. Amino transferase

B. Amino acid dehydratase

C. Transaminase

D. Both A and C

4. In which form ammonia is disposed in the liver?
A. Urea

B. Uric acid

C. Bile

D. All of the above

5. What happens during transamination reaction?

A. Ammonia is liberated

B. Amino group is transferred

C. Amino group is converted

D. all of the above

6. Which of the following acts as a central molecule when transamination and deamination occur simultaneously?

A. Cysteine

B. Glutamate

C. Oxaloacetate

D. Alpha-ketoglutarate

7. Which of the following amino acid do not participate in the transamination reaction?

A. Lysine

B. Valine

C. Threonine

D. Both A and C

8. Which of the following statement is NOT true?
A. Deamination can be oxidative as well non-oxidative
B. Transamination reaction is catalyzed by transaminase only
C. Hydroxy amino acid can be directly demeanated into NH4 ions
D. Serine dehydratase requires PLP co-enzyme

9. What is the other name of alanine transaminase?
A. Glutamate oxaloacetate transaminase
B. Glutamate lactate transaminase
C. Glutamate pyruvate transaminase
D. Glutamate ribulose transaminase

10. what is the other name of aspartate transaminase?
A. Glutamate oxaloacetate transaminase
B. Glutamate lactate transaminase
C. Glutamate pyruvate transaminase
D. Glutamate ribulose transaminase

11. Which of the following is the only amino acid which can be removed through oxidative deamination?
A. Glycine

B. Alanine

C. Aspartate

D. L-glutamate

12. Which of the following requires PLP as co-enzyme?
A. ALT

B. AST

C. Serine dehydrates

D. All of the above

13. Match the following-
a. Transamination 1. Amino acid oxidase
b. Oxidative deamination 2. Amino acid dehydratase
c. Non-oxidative deamination 3. Glutamate dehydrogenase
d. Oxidative deamination 4. Amino transferase

14. Which amino acid can be directly deaminated into NH4 ion?
A. Valine

B. Aspartic acid

C. Tyrosine

D. None of the above

15.The reaction involving glutamate dehydrogenase enzyme reversibly links glutamate metabolism to which cycle?

A. Glycolysis

B. Gluconeogenesis

C. Urea cycle

D. TCA cycle

ANSWERS:-
1. 3
2. Both A and C
3. Both A and C
4. Amino group is transferred
5. Glutamate
6. Both A and C
7. Alpha-ketoglutarate
8. Transamination reaction is catalyzed by transaminase only
9. Glutamate pyruvate transaminase
10. Glutamate oxaloacetate transaminase
11. L-glutamate
12. All of the above
13. a – 4 b – 3 c – 2 d – 1
14. None of the above
15. TCA cycle

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REFERENCE:- Pankaja Naik- Biochemistry; 4^th edition; page no:- 222, 223, 224, 236, 255

2. U Satyanarayana, U Chakrapani-Biochemistry; 4th edition; Page no:- 332-335