After 120 days, RBCs are degraded by reticuloendothelial (RE) system, mainly in liver and spleen. Firstly, hemoglobin is dissociated into heme and globin.
Fate of Globin
The globin may be reutilized for the formation of hemoglobin or degraded to the individual amino acids. The amino acids than undergo their own metabolism, and also participates in fresh globin synthesis.
Degradation of Heme
The catabolism of heme is carried out in small fractions of cells by a complex enzyme system known as heme oxygenase. It occurs in the presence of NADPH and oxygen. Ferric ion, CO and a green pigment known as biliverdin are released. Biliverdin is then converted to red orange pigment known as bilirubin. Bilirubin and its derivatives are collectively known as bile pigments.
The daily bilirubin formation in the body is 250-350 mg. this is yielded not only from hemoglobin but from ineffective erythropoiesis and also from various other heme proteins like cytochrome P450.
Multiple Choice Questions (MCQs)
1. What is the average life span of RBCs?
A. 1 week
B. 1 month
C. 2 years
D. 4 months
2. Where do RE system takes place?
D. Both A and B
3. What happens to the globin part of hemoglobin after its dissociation?
A. Excreted through urine
B. Stored in liver
C. Degraded to its amino acid
D. None of the above
4. What is the complex enzyme system for the catabolism of heme called?
A. Heme dehydrogenase
B. Heme transferase
C. Heme oxygenase
D. Heme synthetase
5. What is the product released after catabolism of heme?
B. Carbon mono-oxide
C. Ferric ion
D. All of the above
6. What is the color of bilirubin?
7. What is the approximate formation of bilirubin in adults?
A. 150-220 mg
C. 250-350 mg
D. 500-700 mg
8. Match the following substrate and its product-
A. Globin 1. Bilirubin
B. Heme 2. Biliverdin
C. Biliverdin 3. Amino acid
9. 1gm of hemoglobin yields how much of bilirubin?
10. What is the color of biliverdin?
11. Complex enzyme system occurs aerobically or anaerobically?
12. Which of the following statement is NOT true?
A. Bilirubin is lipophilic in nature
B. Biliverdin reductase is a ATP dependent soluble enzyme
C. Albumin has 2 binding sites for bilirubin
D. Heme oxygenase enzyme produces biliverdin, ferrous ion and CO.
13. Which form of energy is required for the working of complex enzyme system?
D. None of the above
14. What are the sources that yield bilirubin other than hemoglobin?
A. Ineffective erythropoiesis
B. Cytochrome P450
15. Fill in the blank- bilirubin is the most abundant ——-?
1. 4 months
2. Both A and B
3. Degraded to its amino acid
4. Heme oxygenase
5. All of the above
6. Red orange
8. A – 3 B – 2 C – 1
12. Biliverdin reductase is a ATP dependent soluble enzyme
13. None of the above
REFERENCE:- 1. Pankaja Naik- Biochemistry; 4th edition; page no:- 316-317.
2. U. Satyanarayana, U. Chakrapani; Biochemistry; Elsevier; 4th edition; page no- 214-216.