PORPHYRIN METABOLISM

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PORPHYRIN METABOLISM

• dr Agus Budiman L.

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• Porphyrins are cyclic compounds formed by the
  linkage of four pyrrole rings through methenyl
  bridges.
• Characteristic property of porphyrins is the
  formation of complexes with metal ions e.g. iron
  porphyrins in heme and magnesium porphrins in
  chlorophyll.

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• Examples of natural porphyrins in human and
  animal are hemoglobin, myoglobin, cytochrome c ,
  cytochrome P450, catalase and tryptophan
  pyrrolase.

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• Heme synthesis begins with production of ALA (d
  aminolevulinat) which succinyl-CoA and glycine
  are the sources and ALA synthase and pyridoxal
  phosphate( coenzyme) and occurs at mitochondria
  of living cells. Afterwards with ALA dehydratase
  (in cytosol) to produce porphobilinogen (
  precursor of pyrrole).

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• ALA 1 synthase is the key regulatory enzymes in
  liver that regulate heme synthesis.
• Synthesis of heme from porphobilinogen through
  ferrochelatase.
• Porphyrias are genetic disorders of heme
  metabolism.

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• -In adult human erythrocyte could live for about
  3 months and destroyed mainly in
  reticuloendothelial cells of liver, spleen and
  bone marrow.
• Catabolism of heme carried out in the microsomal
  fractions of cells by heme oxygenase complex.
  Hemin--- heme---biliverdin----bilirubin with
  NADPH.

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• Bilirubin bound with albumin to go to liver.
• Bilirubin uptake in liver with facilitated
  transport system.
• Bilirubin conjugation with glucuronic acid in
  liver( induced by phenobarbital).
• Bilirubin secreted into bile.

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• Three kinds of jaundice (icterus) are
• 1. hemolytic (prehepatic) icterus.
• 2. hepatic icterus.
• 3. obstructive (posthepatic icterus).

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• Unconjugated hyperbilirubinemia
• Neonatal jaundice is a unconjugated
  hyperbilirubinemia because the enzymes UDP
  glucuronyl transferase are reduced.
• Crigler-Najjar syndrome
• Gilbert syndrome
• Toxic Hyperbilirubinemia

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• Conjugated hyperbilirubinemia
• Obstructive of the biliary tree.
• Dubin-Johnson syndrome.
• Rotor syndrome.
• In hepatitis both are unconjugated and
  conjugated hyperbilirubinemia.

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