Catabolism of heme

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A microteaching slide showing the basic steps in catabolism of heme.

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Catabolism of heme

  1. 1. Catabolism of Heme Dr. Prasenjit Mitra Department of Biochemistry SMIMS
  2. 2. Catabolism of heme Heme Bile pigments ( Bilirubin and Biliverdin) Sites Reticulo- endothelial cells of liver, spleen and bone marrow. Sources • Senescent RBC’s (80%) • Other heme containing proteins (Myoglobin, cytochromes) (10%) • Ineffective erythropoiesis (10%) Heme degraded per day – 6gm
  3. 3. Steps of Heme degradation Formation of bilirubin Uptake of bilirubin by liver Conjugation of bilirubin Fate of bilirubin • Secretion of bilirubin into bile • Formation of urobilins in the intestine • Excretion in urine and stool
  4. 4. Formation of Bilirubin Heme Heme oxygenase O2, NADPH + H+ NADP+ Fe3+, CO Biliverdin Biliverdin reductase NADPH + H+ NADP+ Bilirubin Alb Alb Alb Alb Bil Alb RBC Bilirubin-Albumin Complex Macrophage
  5. 5. Uptake & Conjugation of bilirubin in Liver Alb Bil Bilirubin Bilirubin diglucuronide Liver Intestine Bile Rate limiting step Mediated by Multispecific Organ Anion Transporter (MOAT) Induced by phenobarbitone Bilirubin-glucuronyl transferase 2 UDP- glucuronic acid 2 UDP
  6. 6. Fate of Bilirubin Bilirubin diglucuronide Bilirubin Urobilinogen Stercobilinogen Stercobilin  To Feces Urobilinogen Urobilinogen Urobilin To Urine Urobilinogen Intestine Liver Kidney Entero-hepatic circulation
  7. 7. Plasma bilirubin Normal plasma level • Total bilirubin = 0.2-0.8 mg/dl • Unconjugated bilirubin = 0.2-0.6 mg/dl • Conjugated bilirubin = 0-0.2 mg/dl Plasma bilirubin > 1 mg/dl is known as hyperbilirubinemia • Levels between 1-2 mg/dl  Latent jaundice • Level > 2mg/dl Bilirubin diffuses into tissues producing yellowish discoloration of sclera, conjunctiva, skin and mucous membrane resulting in jaundice Jaundice Hemolytic Hepatocellular Obstructive
  8. 8. References • Harper’s Illustrated Biochemistry 29th edition • Lippincott’s Illustrated Biochemistry 5th edition • D M Vasudevan Biochemistry
  9. 9. Thank you…

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