Hemoglobin is a conjugated protein having heme as the prosthetic group and the protein, the globin. It is a Tetrameric protein

1. M.Prasad Naidu
MSc Medical Biochemistry,
Ph.D.Research Scholar

2. Hemoglobin is the red blood pigment exclusively
found in erythrocytes.
Normal range:
Concentration of Hb in blood in
Males is 14 – 16 g/dl
Females is 13 – 15 g/dl

3. Structure:
Tetrameric allosteric protein
 Mol wt 64,450
 Conjugated protein globin +heme
 Globin is the apoprotein part
 Heme is the non-protein part (Prosthetic part)
 Chromo protein
 Example of quaternary structure of protein
 Globular protein
 Consist of 4 poly peptide chain 2 of one type and 2 of
another type ( α2 and β2) held together by
noncovalent bonds.

4.  αhelical conformation constitutes 75% globin
molecules.
 4 of helices are terminated by proline residues.
 Each polypeptide chain contains heme group and
oxygen binding cite.
 Heme consist of protoporphyrin ring and Fe atom
 Fe atom in heme can forms 6 bonds.
 4with N of protoporphyrin
 5th
one imidazole N of proximal histidine.
 In OxyHb , 6th
binds to O2

5. Function:
1.Delivery of O2 from the lungs to the tissues
2. Transport of CO2 and protons (H+
) from tissue to
lungs for expiration.

6. Effect of 2,3,BPG on O2affinity of Hb
levels are higher in younger children compared to
elders.
2,3 BPG is produced in the erythrocytes from an
intermediate (1,3 Bisphosphoglycerate) of glycolysis.
This short pathway is refered as Rapaport Leubering
cycle.

8. Significance of Rapaport leubering cycle
It prevents accumulation of ATP not needed by the
erythrocyte
It supplies 2,3 BPG in oxygen transport which is
required for the Hb function.
2,3 BPG regulates the binding and release of Oxygen
from hemoglobin.
2,3 BPG accounts for about 16% of the non
carbonate buffer value of erythrocyte fluid.

10. HEME
Iron containing compound belonging to the class of
protoporphyrin compounds
Protoporphyrin is composed of 4 pyrrole rings which
are linked by methene (=CH) bridges to from
tetrapyrrole (porphyrin)
4 methyl , two vinyl and two propionate side chain
gps are attached to the porphyrin rings.

11. These can be arranged in 15 different ways
One of these isomers called protoporphyrin IX is
biologically active.
Iron (Fe2+
) held in the center of the protoporphyrin
molecule by co-ordination bonds with the four
nitrogen of the protoporphyrin ring.

14. Iron has 6 valency
 4 bonds are formed b/n iron and nitrogen atoms
of the porphyrin ring system
 5th
bond is formed between nitrogen atom of histidine
residue of the globin polypeptide chain, known as
proximal histidine.
 6th
bond is formed with oxygen

15. Heme Synthesis
Takes place in all cells (occurs to the greatest extent
in the bone marrow and liver)
Occurs both in mitochondria and cytosol.

16. Stages of Heme Synthesis
1.Biosynthesis of - aminolevulinic acid (ALA) from
the precursor glycine and succinyl CoA
2.Formation of porphobilinogen (PBG) from δ amino
levulinic and
3. conversion of the porphobilinogen to the cyclic
tetrapyrrol porphyrin ring and heme.

18. Biosynthesis of δ ALA
1st
step is biosynthesis of Heme
Condensation step (succinyl CoA + glycine)
Rate controlling step in heme synthesis
Occurs in mitochondria

19. Formation of PBG
Occurs in cytosol
2 mol of δ ALA condense to form one mol of porphobilinogen ad
2H2O.
Enzyme is ALA dehydratase , Zn containing enzyme.
Enzyme is inhibited by lead and ALA is excreted in urine (lead
poisoning).

20. Conversion of porphobilirogen to porphyrins and
heme
4 BPG condense head to tail to form a linear
tetrapyrrole.
Enzyme is PBG deaminase.
PBG cylized spontaneouusly to form UPGI and UPG III ,
Enzyme is UPG III cosynthase
UPG III is converted to CPG III by decarboxylation of all
acetate(A) side chain to methyl (M), enzyme is UPG
decarboxylase.
CPG III enter mitochondria , it is converted to PPG III by
CPG oxidase enzyme.

21. This enzyme catalyzed the conversion of two of the
proprionate side chains into vinyl groups by oxidative
decarboxylation.
This enzyme act only on type III coproporphyrinogen
Oxidation of protoporphyrinogen III to protoporphyrin
is catalyzed by another mitochondrial enzyme,
protoporphyrinogen oxidase.

22. Final step involves the incoporation ferrous iron into
protoporphyrin in a reaction catalyzed by
mitochondrial heme synthase or ferrochelatase

23. Regulations of Heme Synthesis
1.ALA synthase allosteric enzyme that catalyzed
controlling step, feed back inhibition by Heme.
2.Iron atom itself may be the active regulatory
species
3.Several substances like steroid hormone metabolites
ethanol, Barbiturate etc induce the synthesis of
hepatic ALA

24. Disorders of Heme biosynthesis
Porphyrias

26. Breakdown of Hemoglobin
RBC life span is 120 days , after this they are
degraded by RE system

27. Fate of Bilirubin

28. Fate of Bilirlubin
Metabolism & excretion of bilirubin occurs in liver &
intestine
 Uptake by liver parenchymal cells
 Conjugation in smooth endoplasmic reticulum in liver
 Secretion of conjugated bilirubin
 Excretion of bilirubin in the form of stercobilin and
urobilinogen through feces and urine respectively

30. Normal concentration of serum bilirubin
 Total bilirubin 0.1 - 1.0 mg/dl
 Conjugated (direct) bilirubin 0.1 – 0.4 mg/dl
 Unconjugated (indirect)bilirubin 0.2 – 0.8 mg/dl
 Bilirubin in blood morethan 1mg/dl is called clinical
hyperbilirubinemia.

31. Hyper bilirubinemia :
 Increased bilirubin production
 Decreased hepatic uptake
 Decreased hepatic conjugation
 Decreased excreation of bilirubin into bile
 Bilirubin accumulates in allthese conditions
approximately 2.2 - 5 mg/dl.
 The skin and sclere appears yellowish due to
deposition of bilirubin in the tissue.
 The condition is called jaundice or Icterus.

32. Jaundice: (Hyperbilirubimia)
acquired or inherited
Conjugated or Unconjugated
4 types
 Hemolytic or prehepatic
 Hepato cellular / Hepatic / intrahepatic
 Obstructive / Post hepatic
 Neonatal / Physiological jaundice

33. Acquired hyperbilirubimia
 Prehepatic or Hemolytic
eg: - sickle haemoglobin (sickle cell anemia)
- deficiency of enzyme glucose 6-phosphate
dehydrogenase.
- Incompatible blood transfusion
Biochemical features
 Increased plasma unconjugated bilirubin
 Increased amount of urobilinogen in urine and
Feces.
 Absence of bilirubin in urine.

34. Intrahepatic / Hepatic / Hepatocellular
Jaundice
Infection (viral hepatitis)
Toxic chemicals (alcohol)
Drugs
cirrhosis
 Uncojugated hyperbilirubinemia and presence of
some conjugated hyperbilirubinemia
Biochemical Features
 Increased plasma concentrtaion of conjugated and
unconjugated bilirubin.
 Decreaed amount of urobilinogen in urine and faeces
 Presence of bilirubin in the urine
 Raise level of alanine transaminase enzyme

35. Posthepatic or Obstructive Jaundice
occurs due to obstruction in the passage of
conjugated bilirubin from the liver cells to the intestine
this condition is also called as cholestasis.
Causes
 Blockage of common bile duct by gallstones
 Carcinoma of the head of the pancreas
 carinoma of the duct

36. Biochemical Features:
Increased conjugated bilirubin in plasma
Absence of urobilinogen in faeces and urine
Presence of bilirubin and bile salts in urine
Raised ALP in plasma

37. Neonatal of physiologic jaundice
 Mild jaundice in the first few days after birth
 Results from an accelerated haemolysis and
immature liver enzyme system for conjugation
 Liver is deficient in enzyme UDP-glucuronyl
transferase.
 Increased unconjugated bilirubin is seen
 If it exceeds 20 – 25 mg/dl it penetrates the BBB
 This results in hyperbilirubinaemic toxic
encephalopathy or kernicterus

38. Inherited hyperbilirubinaemia
 Gilbert’s syndrome
 Crigler Najjar syndrome
 Dubin Johnson syndrome
 Rotor syndrome