This document discusses heme synthesis and degradation. It begins by listing the main heme-containing proteins and their functions. It then describes the structure of heme as containing a ferrous atom in the center of a tetrapyrrole ring. The key steps of heme synthesis and degradation are outlined. The document concludes by discussing disorders associated with errors in heme metabolism, including acute intermittent porphyria and porphyria cutanea tarda.

1. HEME SYNTHESIS AND
DEGRADATION
DR.VINISHA.S.POUSYA
1ST MDS
DEPARTMENT OF ORAL PATHOLOGY

2. Specific learning objectives
At the end of the session, learner should be able to
o List the heme containing proteins and their functions
o Enumerate the structure of heme
o Discuss the steps of heme synthesis
o Enumerate the regulation of heme synthesis
o Discuss the steps of heme degradation
o Enumerate the defects and manifestations of disorders
associated with heme synthesis

3. INTRODUCTION
 Heme is a substance precursive to hemoglobin which is
necessary to bind oxygen to blood stream.
 Heme belongs to hemoproteins family.
 Hemes are components of Hb the red pigment in blood.

4.  Hemoglobins
 Myoglobin
 Cytochromes
 Catalases
 Peroxidase
 Endothelial nitric oxide synthase
Heme containing proteins

5.  Heme is also found in
 Myoglobin
 Cytochromes
 Catalases
 Heme peroxidase
 Endothelial nitric oxide synthase

6. STRUCTURE OF HEME
One ferrous atom in the centre
of the tetrapyrrole ring of
Protoporphyrin IX
Prosthetic group for
Hemoglobin
Myoglobin
Catalyses
Nitric acid synthase
Cytochromes

7. FUNCTIONS
 It has diverse biological functions
 Transportation of diatomic gases
 Chemical catalyses
 Diatomic gas detection
 Electron transfer

8. SYNTHESIS OF HEME

9. DEGRADATION OF HEME

11.  This form of bilurubin is excreted from the liver in
bile.
 Excretion of bilurubin from liver to biliary canaliculi
is an active ,energy dependant and rate limiting
process.
 The intestinal bacteria deconjugate bilurubin
deglucuronide and convert bilurubin into
urobilinogens.

12.  Urobilinogens is absorded by intestinal cells and
transported into the kidneys and excreted as urine.
 The remainder travels down to digestive tract and is
converted in stercobilinogen.
 This is oxidized to stercobilin which is excreted and
is responsible for brown colour of feces.

13. DISORDERS OF HEME
METABOLISM
 Acquired : Lead poisoning Pathophysiology –
Binds to any compound with a sulfhydrl group and
also inhibits multiple enzyme reactions including
those involved in heme biosynthesis (ALA
dehydratase & ferrochelatase)

14.  Congenital- Porphyrias
 In born errors of metabolism associated with the
biosynthesis of heme.
 Characterised by incresed production or production
and excretion of porphyrins and/or their precursors.
 Inherited as autosomal dominant traits.

15. PORPYRIAS
 Hepatic porphyrias
 Erythropoiteic porphyrias
 Porphyrias with both erythropoietic and hepatic
abnormalities
 Triggered by certain drugs, food, chemicals and
even exposure to sun.

16. TYPES
 ACUTE INTERMITTENT PORPHYRIA – caused
due to deficiency of porphobilinogen deaminase,
which is involved in the conversion of
porphobilinogen to uroporphyrinogen III
 Patients have neuropsychiatric symptoms and
abdominal pain.

17.  PORPHYRIA CUTANEA TARDA – caused due to
the deficiency uroporphyrinogen decarboxylase,
which is involved in the conversion of
uroporphyrinigen III to coproporphyrinogen III
 Patients will be photosensitive(cutaneous
photosensitivity)

18. REFERENCES
 TEXTBOOK OF BIOCHEMISTRY BY VASUDEVAN
 PICTURE SOURCE : WIKIPEDIA