1. Metabolism of arginine

Arginine is a semi-essential amino acid. It can be synthesized in the body but not in that much quantity that it can satisfy the body requirements. Thus it is an amino acid, which is required for growth but not for maintenance of the body.

Synthesis of arginine:- Arginine is synthesized from glutamate.

• Glutamate is reduced to glutamate-gamma-semialdehyde.
• Transamination of glutamate-gamma-semialdehyde yields ornithine (an intermediate of urea cycle). The reactions of urea cycle further converts ornithine to arginine.

Degradation of arginine:-  Breakdown of arginine by arginase enzyme forms urea and ornithine. If ornithine is present in considerable amounts then it is used in urea cycle; but if it is present in excess after its requirement in urea cycle, then it is converted into glutamate-semialdehyde. Glutamate semialdehyde is then reduced back to glutamate. 

Significance of arginine

1. It takes part in formation of urea
2. It is involved in the synthesis of creatine
3. Nitric oxide is synthesized by arginine

Metabolism of histidine

It is a glucogenic semi-essential amino acid Degradation of histidine Degradation process mainly occurs in liver.

• After a series of reactions, histidine is converted to form-imino glutamate (FIGLU).
• The rest of the reaction transfer the form-imino group of FIGLU to form tetrahydrofolate (THF)to form N-5 form-imino THF and leaves L-glutamate.
• N-5 form-imino THF is used in one-carbon metabolism

Image is taken  only for education purpose from slideshare of Dr. Dhiraj Trivedi

Importance of histidine

1. After its decarboxylation, it forms histamine which reduces BP and also increases the secretion of gastric juice.
2. It is involved in the formation of biologically important peptides like carnosine and anserine.

Metabolism of lysine

Lysine is a glucogenic as well as ketogenic essential amino acid. It contains two amino group but none of the group undergoes direct transamination.

Catabolism of lysine:-  Lysine Is degraded by a complex pathway in which saccharopine, alpha-ketoadipate and crotonyl-CoA are intermediates. Lysine at last generates acetyl-CoA.

Significance of lysine

It is involved in the synthesis of carnitine. Carnitine works for the transport of fatty acid across mitochondria membrane.

Multiple choice questions (MCQs)

1. arginine is nutritionally divided as which type of amino acid?

A. Essential amino acid

B. Non-essential amino acid

C. Semi-essential amino acid

D. Both A and C

2. is arginine essential for the growth or maintenance of the body? A. Growth

B. Maintenance

C. Both

D. None

3. arginine is synthesized from which compound?

A. Lysine

B. Glutamate

C. Histamine

D. Lactate

4. in which condition, arginine on catabolism yields glutamate again?

A. If ornithine is present in excess

B. Urea is present in excess

C. Both

D. None

5. What compound is released on the conversion of glutamate semi-aldehyde to ornithine?

A. CO2

B. Oxaloacetate

C. Water

D. Keto acid

6. Histidine is nutritionally divided as which type of amino acid?

A. Essential amino acid

B. Non-essential amino acid

C. Semi-essential amino acid

D. Both A and C

7. Arginine acts as a substrate for the production of which compound?

A. Nitric acid

B. Nitric oxide

C. Nitrous oxide

D. both B and C 

8. Match the following enzyme and its product-

a. Histidase 1. urocanate

b. Urocanase 2. imidaziolone

c. Saccharopin dehydrogenase 3. Alpha-aminodipate

d. Arginase 4. urea

9. Which compound is used in one-carbon metabolism?

A. Arginine

B. Glutamate

C. Histidine

D. N-5 form-imino THF

10. Excretion of FIGLU provides a diagnostic test for which type of vitamin deficiency?

A. Vitamin B1

B. Vitamin B9

C. Vitamin C

D. Vitamin K

11. Which amino group of lysine undergoes direct transamination? A. 1st amino group

B. 2nd amino group

C. Both

D. None of the above

12. Which of the following statement is NOT true?

A. Arginine is non-essential amino acid

B. Arginine takes part in formation of urea

C. Catabolism of histidine occurs in liver

D. Lysine is essential amino acid

13. Which compound Is converted to glutamate first and then metabolized?

A. Histidine

B. proline

C. arginine

D. All of the above

14. Which of the following compound reduces BP?

A. Arginine

B. Glutamate

C. Histidine

D. Histamine

15. Which compound is involved in the synthesis of creatine?

A. Arginine

B. Glutamate

C. Histidine

D. Lysine

ANSWERS:-

1. Semi-essential amino acid

2. Growth

3. Glutamate

4. If ornithine is in excess

5. Keto acid

6. Semi-essential amino acid

7. Nitric oxide

8. a – 1 b – 2 c- 3 d – 4

9. N-5 form-imino THF

10. Vitamin B9

11. None of the above

12. Arginine is non-essential amino acid

13. All of the above

14. Histamine

15. Arginine

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REFERENCE:- 1. Pankaja Naik- Biochemistry; 4^th edition; page no:- 294-296.  

2. U Satyanarayana, U Chakrapani-Biochemistry; 4th edition; Page no:- 366-369.