EXPORT CITATION

Chapter-21 Heme Synthesis and Breakdown

BOOK TITLE: Textbook of Biochemistry for Medical Students

Author
1. Vasudevan DM
2. S Sreekumari
3. Vaidyanathan Kannan
ISBN
9789350250167
DOI
10.5005/jp/books/11359_21
Edition
6/e
Publishing Year
2011
Pages
12
Author Affiliations
1. Faculty of Medicine, Amrita Vishwa Vidyapeetham, (Amrita University), Kochi, Kerala, Formerly Principal, College of Medicine, Amrita, Kerala; Formerly, Dean, Sikkim Manipal Institute of Medical Sciences, Gangtok, Sikkim, Amrita Vishwa Vidyapeetham (Deemed University), Cochin, Kerala, E-mail: dmvasudevan@aims.amrita.edu, PG Programs and Research College of Medicine, Amrita Institute of Medical Sciences, Kochi, Kerala, India, College of Medicine, Amrita Institute of Medical Sciences, Kochi, Kerala, India; Sikkim Manipal Institute of Medical Sciences, Gangtok, Sikkim, India
2. Jubilee Mission Medical College, Trissur, Kerala, Sree Gokulam Medical College and Research Foundation, Thiruvananthapuram, Kerala, India, Jubilee Mission Medical College and Research Institute, Thrissur, Kerala, India, Government Medical College, Thrissur and Thiruvananthapuram, Kerala, India; Sree Gokulam Medical College and Research Foundation, Thiruvananthapuram, Kerala, India; Jubilee Mission Medical College and Research Institute, Thrissur, Kerala, India
3. Amrita Institute of Medical Sciences, Kochi, Kerala, India, Pushpagiri Institute of Medical Sciences and Research Centre, Thiruvalla, Kerala, India, Believers Church Medical College and Hospital, Thiruvalla, Kerala, India
Chapter keywords

Abstract

Hemoglobin—the oxygen transporter is a 67 KD tetrameric conjugated protein with heme as prosthetic group and globin polypeptide (2 alpha and 2 beta chains). Heme is a derivative of porphyrin, which is a cyclic compound formed by the fusion of 4 pyrrole rings, linked by methenyl bridges and has an iron atom at its center. Regulation of heme synthesis is by repression of ALA synthase by heme and high cellular concentration of glucose prevents ALA synthase induction. Barbiturates induce the enzyme. ALA synthase is also allosterically inhibited by hematin. Porphyrias are the class of metabolic disorders associated with heme synthesis. AIP occurs due to deficiency of PBG deaminase. Congenital erythropoietic porphyria is due to imbalance in activities of uroporphyrinogen I synthase and co-synthase. Acquired porphyries result from lead poisoning. Normal plasma bilirubin levels range from 0.2 – 0.8 mg/dL and can be detected by van den Berg’s test. Congenital hyperbilirubinemias include Gilbert’s disease where bilirubin uptake is defective, Crigler–Najjar syndrome where conjugation is defective Dublin Johnson syndrome where defect is in excretion of conjugated bilirubin. Acquired hyperbilirubinemias or Jaundice may be physiological jaundice, hemolytic jaundice, hepatocellular jaundice and obstructive jaundice.

© 2019 Jaypee Brothers Medical Publishers (P) LTD.   |   All Rights Reserved