Hemoglobin is a globular protein in red blood cells that transports oxygen throughout the body. It is composed of four polypeptide subunits, two alpha chains and two beta chains, as well as an iron-containing heme group that binds oxygen. Hemoglobin levels in healthy individuals typically range from 13-16 g/dL. Hemoglobin is synthesized through a series of enzymatic steps that convert the substrates glycine and succinyl-CoA into protoporphyrin, followed by insertion of ferrous iron to form heme. Heme gives hemoglobin its red color and allows it to carry oxygen through reversible binding to iron at the center of the porphyrin ring. Precise regulation of heme synthesis is

1. HEMOGLOBIN structure and
metabolism
Dr Anurag Yadav
MBBS, MD
Assistant Professor
Department of Biochemistry
Instagram page –biochem365
Email: dranurag.y.m@gmail.com

2. Structure of Hemoglobin
 Normal level of Hemoglobin (Hb) in blood;
 males: 14–16 g/dL.
 females:13–15 g/dL.
 Hb is globular in shape.
 The adult Hb (HbA) has 2 alpha chains and 2
beta chains.
 Molecular weight of HbA is 67,000 Daltons

4. GENETICS OF GLOBIN

5. Other Hemoglobins in normal
adults (non pathological)
Hemoglobin Structure %
A α2 β2 92%
A2 α2 δ2 2.5%
A1C α2 (β-N-glucose) 3%
F α2 γ2 <1%
Gower-1 ζ2 ε2 0*
Gower-2 α2 ε2 0*
Portland ζ2 γ2 0*
* Indicates early embryonic form not seen in adults

6. Normal Hemoglobin Structure
 Hemoglobin A is a tetramer composed of 4
subunits:
 2α (141aa) and 2β (146aa)
 Each subunit has a ring (porphyrin ring) which
holds an iron molecule.
 This is the binding site of oxygen.
 There are 36 histidine residues in Hb
molecule; these are important in buffering
action.

7. Normal Hemoglobin Structure
Hemoglobin tetramer

8. Normal Hemoglobin Structure
Fe
O
O
The oxygen atom binds to the Fe atom
perpendicular to the porphyrin ring
Porphyrin ring O2 binding site

9. Hemoglobin Function
 The function of the Hemoglobin molecule is to pick
up oxygen in the lung and deliver it to the tissues
utilizing none of the oxygen along the way.
 Buffering action.

10. Hemoglobin Function
 The normal hemoglobin molecule is well suited for its
function
 Allows for O2 to be picked up at high O2 tension in the lung
and delivered to the tissues at low O2 tension.
 The oxygen binding is cooperative:
 As each O2 binds to hemoglobin, the molecule undergoes a
conformational change increasing the O2 affinity for the remaining
subunits.
 This creates the sigmoidal oxygen dissociation curve

13. Normal Hemoglobin Function
The hemoglobin dissociation curve

15. Normal Hemoglobin Function
Many variables influence the dissociation curve:
pH:
• An increase in pH (dec. CO2) shifts the curve to the left (increased O2) affinity
• A decrease in pH (inc. CO2) shifts the curve to the right (decreased O2 ) affinity
Temperature:
• Increased temp with increased metabolic demands causes decreased O2 affinity
(right shift) and increased O2 delivery
2,3 DPG (2,3-diphosphoglycerate):
• Lowers O2 affinity by preferentially binding to Beta chain of deoxyhemoglobin,
stabilizing it and reduces the intracellular pH
• As hemoglobin concentration decreases, 2,3 DPG increases, allowing more O2
to be unloaded

16. Hemoglobin variant
 Hemoglobin variants are mutant forms of
hemoglobin in a population (usually of humans),
caused by variations in genetics.
 Some hemoglobin variants such as sickle-cell
anemia causes diseases, hence they are
hemoglobinopathies.
 Other variants cause no detectable disease, thus
considered non-pathological variants.

17. Other Hemoglobins in normal
adults (non pathological)
Hemoglobin Structure %
A α2 β2 92%
A2 α2 δ2 2.5%
A1C α2 (β-N-glucose) 3%
F α2 γ2 <1%
Gower-1 ζ2 ε2 0*
Gower-2 α2 ε2 0*
Portland ζ2 γ2 0*
* Indicates early embryonic form not seen in adults

18. Hemoglobin Abnormalities
• Structural or qualitative: The amino acid
sequence is altered because of incorrect
DNA code (Hemoglobinopathy).
• Quantitative: Production of one or more
globin chains is reduced or absent
(Thalassemia).
• Hereditary persistence of Fetal
Hemoglobin (HPFH): Complete or partial
failure of γ globin to switch to β globin.
There are 3
main
categories of
inherited
Hemoglobin
abnormalities:

19. Hemoglobinopathies
 Disorders caused due to mutations in the genes
for globin chains, resulting in hemoglobin
molecules with abnormal structure and function
 Autosomal recessive
 1. Structural variants
 2. Thalassemias
 3. Hereditory persistance of fetal Hb

20. Structural variants
 Usually due to : point mutations /base
substitutions , amino acid substitutions in
alpha/beta chains.
 Mutations of : structural
genes/deletions/termination genes.
 About 750 are known; few have clinical
manifestations.
 Structural variants causing sickling disease : HbS,

21. HbS
 Normal : AA
 Heterozygous : AS : Sickle cell trait
 Homozygous : SS : Sickle cell disease
 Beta-6 : Glu replaced by Val

22. HbS

23. HbS
 Effects of HbS :
 Polymerization of HbS molecules in
deoxygenated state
 Sickle shape of RBCs.

24. Polymerization of deoxy HbS &
Sickling

25. Effects of sickle shaped RBCs

26. Consequences of sickling
 Vaso-occlusion
 Hemolysis ;
 Jaundice
 Anaemia
 Splenomegaly
 Increased susceptibility to infections
 Hypoxia , infarctions
 Organ Failure
 Bone pains

27. Sickle Crises

28. Lab diagnosis of Sickle cell disease
/trait
 Hb, CBC
 Peripheral Smear – Sickle shaped RBCs
 Hemoglobin electrophoresis : showing S band
between A and A2.
 Solubility Test : Precipitation of HbS in the
presence of sodium dithionite
 HbS % : > 70-80% in sickle cell disease

30. Abnormal Hb in Other sickling
diseases
 Hb C : Beta-6 : Glu replaced by Lys
 HbD(Punjab) : beta-121 : Glu replaced by Gln
-- HbE : Beta-26 : Glu replaced by Lys
-- HbSC
-- HbSE

31. Hemoglobins with reduced Oxygen
Affinity
 Hb Kansas : beta-102 : Asn replaced by Thr
 HbM (Hb Boston) : alpha-58 His replaced by Tyr :
oxidation of iron
 Cyanosis

32. Hb with increased oxygen affinity
 Mutations causing affecting interaction of heme
with globin
 Eg. Hb Reiner :Beta-145 Tyr replaced by Cys
 Polycythemia

33. Elongated globin chains
 Chain termination mutations
 Eg. Hb constant spring :alpha-chain with 172
amino acids

34. Thalassemia
 Inherited defects in synthesis of globin chains;
reduced rate of synthesis of one or more globin
chains
 Result in : Inadequate production of Hb;
unbalanced accumulation of globin chains
 Alpha, beta, delta, delta-beta thalassemias.

35. Alpha-thalassemia
 Normal (α α/ α α)
 (- α/ α α) : silent carrier
 (- α/ - α) or (- -/α α) : : alpha thalassemia trait
: mild hypochromic microcytic anaemia
 (- -/ - α) : HbH disease (β4) : mild
hypochromic microcytic anaemia
 (- -/ - -) : Hb Bart’s (γ4) – hydrops fetalis,
death in utero or shortly after birth

36. Alpha thalassemia
 HbH disease : microcytic anaemia, splenomegaly,
jaundice, iron overload
 HbH : moving ahead of A in electrophoresis
 HbH : Inclusion bodies stained by brilliant cresyl
blue in peripheral smear.

37. Beta thalassemia
 β+ / β0 thalassemia
 β+ : thalassemia minor / intermedia
 β0 : thalassemia major
 Thalassemia minor : mild microcytic anaemia,
Mild elevation of HbF, increase in HbA2.
 Thalassemia Major : High HbF, Severe
microcytic anaemia; Blood transfusion
required.

38. Clinical manifestations
 bone marrow hyperexpansion; Thalassemia Facie
 Splenomegaly
 Severe Anaemia
 Multiple organ dysfinction
 Premature death

39. Splenomegaly

40. “Hair on end” apperance of skull

41. Beta thalassemia- lab diagnosis
 1. Hb, blood count, MCV, MCH, MCHC
 2. Peripheral Smear
 3. Hb electrophoresis
 4. Estimation of HbF : alkali denaturation method/
HPLC
 5. HbA2 : Estimation by HPLC

44. Metabolism of Heme
Dr Anurag Yadav
Assistant Professor
Department of Biochemistry

45.  What is Heme?
 Heme containing proteins
 What are porphyrins?
 Heme biosynthesis

46. Structure of Heme
Heme is made up of a protoporphorin III ring and an
iron ion in the ferrous (Fe II) oxidation state.
Heme = Protoporphyrin III --- Fe+2

47. Human and Animal
Hemoproteins
 Hemoglobin - Transport of oxygen in blood
 Myoglobin - Storage of oxygen in muscle
 Cytochrome c - Involvement in electron
transport chain
 Cytochrome P450 - Hydroxylation of
xenobiotics
 Catalase - Degradation of hydrogen peroxide
 Tryptophan pyrrolase - Oxidation of
tryptophan

48. Porphyrins
Porphyrins are cyclic compounds formed by the
linkage of four pyrrole rings through methyne
(=HC—) bridges
Pyrrole Ring

49. c
c
c
c
N
c
c
c
c
c
c
c
c
c
c
c c
N
N
N
c c
c c
R R
R
R
R
R
R
R

50. The porphyrins are compounds in which various
side chains are substituted for the eight hydrogen
atoms numbered in the porphyrin nucleus
1
I
II
III
IV
2
4
5
6
8
7
3

51. Types (I and III)
Two types (I and III) are found in nature
A porphyrin with a completely symmetric arrangement
of the substituents is classified as a type I porphyrin.
A porphyrin with this type of asymmetric substitution
is classified as a type III porphyrin.

52. examples
I
II
III
IV
P
A
P
A
A
P
A
P
I
II
III
IV
P
A
P
A
A
P
P
A
Uroporphyrin I Uroporphyrin III
A = acetate = —CH2 COOH
P= propionate = —CH2 CH2 COOH

53. examples
I
II
III
IV
P
M
P
M
M
P
M
P
I
II
III
IV
P
M
P
M
M
P
P
M
Coproporphyrin I Coproporphyrin III
M = methyl = —CH3
P= propionate = —CH2 CH2 COOH

54. examples
I
II
III
IV
V
M
V
M
M
P
M
P
I
II
III
IV
V
M
V
M
M
P
P
M
Protoporphyrin I Protoporphyrin III or (IX)
M = methyl = —CH3
P= propionate = —CH2 CH2 COOH
V = venyl = —CH=CH2

55. STRUCTURE OF HEME
 heme, a cyclic tetrapyrrole consisting of four
molecules of pyrrole linked by -methyne bridges.
 The substituent groups of heme methyl (M), vinyl
(V), and propionate (Pr) are arranged
asymmetrically.
 One atom of ferrous iron (Fe2+ ) resides at the
center of the planar tetrapyrrole

56. c
c
c
c
N
c
c
c
c
c
c
c
c
c
c
c c
N
N
N
c c
c c
methyl venyl
venyl
methyl
propionate
methyl
propionate
methyl
Fe 2+

57. Heme biosynthesis
 SITE:
 occurs in most mammalian cells except mature
erythrocytes (which do not contain mitochondria).
 approximately 85% occurs in the bone marrow
and
 majority of the remainder in hepatocytes.
SUBCELLULAR SITE:
Partly in cytosol and partly in mitochondria

58.  Substrate required for Heme Synthesis
 Succinyl CoA
 Glycine

59. STEPS in Heme Synthesis:
 Step1: ALA Synthesis
 Step 2: Formation of PBG (Porphobilinogen)
 Step 3: Formation of UPF (Uroporphyrinogen)
 Step 4: Synthesis of CPG (Coproporphyrinogen)
 Step 5: Synthesis of PPG (Protoporphyrinogen)
 Step 6: Generation of PP (Protoporphyrinogen)
 Step 7: Generation of Heme.

60. Step 1: ALA Synthesis

61. Step 2: Formation of PBG
(Porphobilinogen)
 Cytoplas
m
 Inhibited
by Lead
ALA dehydratase

62. Step 3: Formation of UPG
(Uroporphyrinogen)
PBG-deaminase
(Uroporphyrin I synthase)
uroporphyrinogen III synthase

63. Step 4: Synthesis of CPG
(Coproporphyrinogen)
uroporphyrinogen decarboxylase.

64. Step 5: Synthesis of PPG
(Protoporphyrinogen)
coproporphyrinogen oxidase

65. Step 6: Generation of PP
(Protoporphyrinogen)
 Occur in mitochondria
 The methylene bridges (–CH2) are oxidized to
methenyl bridges (–CH=) and colored porphyrins
are formed
protoporphyrinogen oxidase

66. Step 7: Generation of Heme.
 The last step in the formation
of heme is the attachment of
ferrous iron to the
protoporphyrin.
 The enzyme is heme
synthase or ferrochelatase,
which is also located in
mitochondria.

67.  Iron atom is co-ordinately linked with 5 nitrogen
atoms (4 nitrogen of pyrrole rings of
protoporphyrin and 1st nitrogen atom of a
histidine residue of globin).
 The remaining valency of iron atom is satisfied
with water or oxygen atom

68.  When the ferrous iron (Fe++) in heme gets
oxidized to ferric (Fe+++) form, hematin is
formed, which loses the property of carrying the
oxygen.

70. Regulation of heme
 ALA synthase is regulated by repression
mechanism.
 ALA synthase is also allosterically inhibited by
hematin.
 The compartmentalization of the enzymes.
 Drugs like barbiturates induce heme synthesis.
 The steps catalyzed by ferrochelatase and ALA
dehydratase are inhibited by lead.
 INH decrease availability of PLP.
 High cellular concentration of glucose prevents
induction of ALA synthase.

71.  Porphyrias
 Functions of Hb
 Abnormal Hemoglobins
 Degradation of Heme
 Jaundice
 Liver Function Tests

72. PORPHYRIAS
1. WHAT ?
 A group of rare disorders caused by deficiency of
enzymes of the heme biosynthetic pathway.

73. ALA
+
PPG III
UPG III
PROTOPORPHYRIA
GLYCINE
PBG
HEME
SUCCINYL CO A
ALA
PROTOPORPHYRIN III
ALA DEHYDRATASE
3 PBG
HMB
CPG III
CONGENITAL ERYTHROPOIETIC PORPHYRI
UPG III COSYNTHASE
UPG DECARBOXYLASE
CPG OXIDASE
ACCUTE INTERMITTENT PORPHYRIA
PBG DEAMINASE
PPG OXIDASE
FERROCHELATASE
PORPHYRIA CUTANEA TARDA
VARIEGATE PORPHYRIA
HERIDITORY COPROPORPHYRIA
ALA DEHYDRATASE DEFICIENCY
X-linked sideroblastic anemia

74. 2. MODE OF INHERITANCE
 inherited in an autosomal dominant manner, with
the exception of
congenital erythropoietic porphyria,
which is inherited in a recessive mode.
 thus, affected individuals have 50% normal levels
of the enzymes, and can still synthesize some
heme

75. 3.classification
 The porphyrias can be classified on the basis of
1. the organs or cells that are most affected.
 hepatic
 erythropoietic
2. Clinical presentation of symptoms
 Acute
 Nonacute

76. Classification based on organ affected
hepatic
ALA dehydratase deficient porphyria
Acute intermittent porphyria
Porphyria cutanea tarda
Hereditary coproporphyria
Variegate porphyria
erythropoietic
Congenital erythropoietic porphyria
Protoporphyria

77. Classification based on clinical presentation
 Acute
 ALA dehydratase deficient porphyria
 Acute intermittent porphyria
 Hereditary coproporphyria
 Variegate porphyria
 Nonacute
 Porphyria cutanea tarda
 Congenital erythropoietic porphyria
 Protoporphyria

78. 4. Signs and symptoms
the signs and symptoms of porphyria result from
either
a deficiency of metabolic products beyond the
enzymatic block or
from an accumulation of metabolites behind the
block.

79. Accumulation of porphyrinogens
Oxidation
Excited porphyrins
oxygen radicals
Damaged lysosomes release their degradative enzymes
injure lysosomes and other organelles
molecular oxygen
Visible light of about 400 nm
Oxidized porphyrin derivatives
skin damage, including scarring.
Enzyme block later in the pathway
photosensitivity

81. 5.Diagnostic tests
 in urine
ALA PBG, Uroporphyrin, Coproporphyrin
 In feces
Coproporphyrin, protoporphyrin
 In blood
protoporphyrin
 Assay of the activity of enzymes OF HEME
SYNTHESIS in red blood cells

82. 6. TREATMENT
 administration of hemin,
which provides negative feedback for the heme
biosynthetic pathway,
and therefore, prevents accumulation of heme
precursors
 Avoiding disease are triggering agents such as
certain drugs,
alcohol,
hormones,
stress and infections,
and also exposure to sun.

83. 7.IMPORTANCE
 They are not prevalent, but it is important to consider
them in certain circumstances
 eg, in the differential diagnosis of
abdominal pain and of a variety of neuropsychiatric
findings

85. Catabolism of Heme

86. Catabolism of Heme
 in 1 day, a 70-kg human turns over approximately
6 g of hemoglobin.
 When hemoglobin is destroyed in the body,
globin is degraded to its constituent amino acids,
which are reused,
 and the iron of heme enters the iron pool, also
for reuse.
 The iron-free porphyrin portion of heme is
also degraded.

87. Biliverdin
catabolism
Globin
Bilirubin
Hemoglobin
Iron pool
Heme
Fe +2
Amino acid pool
Hemoglobin
ineffective
erythropoiesis
heme proteins

88. Metabolism of bilirubin
1. Catabolism of Heme (Formation of Bilirubin)
2. Transport of Bilirubin in plasma
3. Uptake of bilirubin by liver parenchymal cells.
4. Conjugation of bilirubin with glucuronate in the
endoplasmic reticulum, and
5. Secretion of conjugated bilirubin into the bile.
6. Formation of Urobilinogen

89. 1.Catabolism of Heme (Formation of Bilirubin)
6. . Formation of Urobilinogen
2.Transport of Bilirubin in plasma
a
. 3. Uptake of bilirubin by liver parenchymal cells.
4. Conjugation of bilirubin with glucuronate
5 Secretion of conjugated bilirubin into the bile..

91. 1. Catabolism of Heme
(formation of Bilirubin)
Site:
mainly in the reticuloendothelial cells of the liver,
spleen, and bone marrow.
Subcellular site:
microsomal fraction of cell

92. Fe 3+
NADPH,H+
HEME
BILIVERDIN
Heme
Oxygenase
system
NADPH,H+
BILIRUBIN
O 2
CO
NADP+
NADP+
Biliverdin Reductase
Hemoglobin
ineffective
erythropoiesis
heme proteins

93.  It is estimated that 1 g of hemoglobin yields 35 mg of
bilirubin.
 The daily bilirubin formation in human adults is
approximately 250–350 mg,
 deriving mainly from
 hemoglobin
 ineffective erythropoiesis and from
 various other heme proteins such as cytochrome
P450.

94. 2. Transport of Bilirubin in plasma
 Bilirubin formed in peripheral tissues is transported
to the liver by plasma albumin.
 Each molecule of albumin has one high-affinity site
and one low-affinity site for bilirubin.
 In 100 mL of plasma, approximately 25 mg of
bilirubin can be tightly bound to albumin at its high-
affinity site.
.

95. 3. Uptake of Bilirubin by Liver
 bilirubin is taken up at the sinusoidal surface of the
hepatocytes by a carrier-mediated saturable system.
 Once bilirubin enters the hepatocytes, it binds to
 Ligandin and
 protein Y.

96. 4. Conjugation of Bilirubin with
Glucuronic Acid
Subcellular site
endoplasmic reticulum
 Bilirubin is nonpolar. Hepatocytes convert
bilirubin to a polar form, which is readily excreted
in the bile, by adding glucuronic acid molecules to
it.
This process is called conjugation

98. The conjugation of bilirubin is catalyzed by bilirubin-
UDP Glucuronyl Transferase (bilirubin-UGT).
 Bilirubin-UGT activity can be induced by
 a number of clinically useful drugs, including
phenobarbital.

99. 5. Secretion of Bilirubin into
Bile
 Secretion of conjugated bilirubin into the bile
occurs by an active transport mechanism,
 which is rate limiting for the entire process of
hepatic bilirubin metabolism.
 The protein involved is MRP-2 (multidrug-
resistance like protein 2), also called multispecific
organic anion transporter (MOAT).

100.  The hepatic transport of conjugated bilirubin into
the bile is inducible by
 those same drugs that are capable of inducing
the conjugation of bilirubin.
 Thus, the conjugation and excretion systems for
bilirubin behave as a coordinated functional unit.

101. 6. Reduction of Conjugated
Bilirubin to Urobilinogen
In terminal ileum and the large intestine,
the glucuronides are removed by specific bacterial
enzymes ( -glucuronidases),
 the pigment is subsequently reduced by the fecal
flora to colorless urobilinogens.
 a small fraction of the urobilinogens is
reabsorbed and reexcreted through the liver to
constitute the enterohepatic urobilinogen
cycle.

102. In terminal ileum and the large intestine
Bilirubin diglucuronide
Reduction
0–4 mg/24 h
glucuronides
glucuronidases
urobilinogens
enterohepatic
urobilinogen cycle.
Blood
40–280
mg/24 h
urine
Liver
feces
absorption

103. Normal level
In serum
Total Bilirubin - 0.2 -1.0 mg/dl
Unconjugated bilirubin – 0.2 - 0.8 mg/dl
Conjugated bilirubin – 0 - 0.2 mg/dl
In urine :
Bilirubin is absent
Urobilinogen - 0–4 mg/24 h
In feces
Urobilinogen- 40–280 mg/24 h

105. JAUNDICE
 Yellowish discoloration of skin and sclera.

111. Dr Anurag Yadav
MBBS, MD
Assistant Professor
Department of Biochemistry
Instagram page –biochem365
YouTube – Dr Biochem365
Email: dranurag.y.m@gmail.com