Learning Objectives
 Fetal Hb
 Carboxy Hb
 Met-Hb
 Hemoglobinopathies
 Sickle cell anemia, thalassemia,
myoglobin, anemias
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Fetal Hemoglobin
 Fetal hemoglobin has 2 α and 2 γ chains
 The gamma chain is 72% identical to the
β chain (146 a.a. in gamma chain).
 A His involved in binding to 2,3-BPG is
replaced with Ser. Thus, fetal Hb has two
less + charge than adult Hb.
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Differences in HbA and HbF
 Increased solubility of deoxy-Hb
 Slower electrophoretic mobility
 Increased resistance of HbF to alkali
denaturation
 Decreased interaction with 2,3-BPG
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The binding affinity of fetal hemoglobin for 2,3BPG is significantly lower than that of adult
hemoglobin
• Thus, the O2 saturation capacity of fetal
hemoglobin is greater than that of adult
hemoglobin
• This allows for the transfer of maternal O2 to
the developing fetus
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ODC of HbF------ left
Synthesis starts by 7th week of gestation.
At birth, 80 % of Hb is fetal Hb.
During the first six month of life, it decreases
to about 5 % of total.
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Hb A2
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Normal adult Hb
About 2%
2alpha and 2delta chains
Isoelectric pH = 6.85
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Derivatives of haemoglobin
Haemoglobin can form the following
derivatives :
1. Oxyhaemoglobin
2. Carboxyhaemoglobin
3. Methaemoglobin
4. Sulphaemoglobin
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Oxyhaemoglobin
 This is the oxygenated form of haemoglobin
 It is bright red in colour
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1.Carboxyhaemoglobin
 Haemoglobin combines with carbon
monoxide to form carboxyhaemoglobin
 Affinity of haemoglobin for carbon
monoxide is 200 times that for oxygen
 Carboxyhaemoglogin is cherry red in colour
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2. Methemoglobin
 Certain drugs and chemicals e.g.sulphonamides,
antipyrine, nitrites, nitrobenzene etc. can oxidise
the ferrous iron of hemoglobin to ferric iron
 Haemoglobin is converted into methhaemoglobin,which is brownish red in colour
 Methaemoglobin cannot combine with oxygen
 Glutathione dependent Met-Hb-reductase accounts
for the rest 5% activity
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2- A Met-Hemoglobinemias
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Less than 1% met-Hb
Markedly decreased capacity of oxygen
binding and transport
Increased met-Hb(met-hemoglobinemia)---cyanosis
Causes may be congenital or acquired
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2B-Congenital met -hemoglobinemia
 Cyt b5 reductase deficiency is characterized
by cyanosis from birth
 Oral administration of methylene blue,100300mg/day or ascorbic acid 200-500mg/day
decreases met-Hb level to 5-10% and
reversre the cyanosis
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2C- acquired or toxic metHemoglobinemia
 May develop by intake of water containing
nitrates or due to absorption of aniline dyes
 Some drugs: acetaminophen, phenacetin,
sulphanilamide, amylnitrite and Sod.
Nitropruside
 G-6-PDH deficiency:
-NADPH is Not available in RBC
-treatment- i.v. leukomethylene blue 2mg/kg
which will substitute for NADPH
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2D- Lab. analysis
 Ferricyanid oxy and deoxy-Hb to met-Hb
 Colour changes to dark brown and
absorption spectra show a band in red with
its centre 633 nm
 Band of oxy-Hb persist
 Sod.hydro sulphite or dithionite reconverts
met-Hb to oxy-Hb
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HEMIN CRYSTALS
 When iron is oxidised to Fe +++. It can
combine with negatively charged Cl – to
form hemin.
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HEMIN CRYSTAL STRUCTURE
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Sulf-hemoglobinemia
 When H2S acts on oxy-Hb, sulf-Hb is
produced
 By the intake of drugs like sulphonamides,
phenacetin, acetanilide,dapsone etc.
 Can not converted back to oxy-hb
 Seen as basophilic stippling of
RBC,
throughout its life span
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Sulf-hemoglobin
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Haemoglobinopathies
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Abnormal Haemoglobins
 Several abnormal haemoglobins are formed
due to mutations in the genes encoding
polypeptide chains of haemoglobin
 Often, a single amino acid is substituted
Hundreds of abnormal haemoglobins have
been discovered, most of which are capable
of normal or near-normal functioning
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 In some cases, when the amino acid
substitution occurs in a critical region of the
molecule, the functioning of haemoglobin is
impaired
 The diseases resulting from the synthesis
of functionally abnormal haemoglobins are
termed as haemoglobinopathies
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 Some important abnormal haemoglobins
and the diseases resulting from them are:
 • Haemoglobin S
 • Haemoglobin M
 • Thalassaemia
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Haemoglobin S
 This is formed when the glutamate residue
at position 6 in the β chain is replaced by
valine
 This amino acid residue is present on the
surface of the haemoglobin molecule
 Replacement of the polar glutamate by
nonpolar valine alters the surface
properties of the haemoglobin molecule
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 The nonpolar valine residue on the surface
of one molecule attracts the nonpolar
residue of another haemoglobin molecule
 This starts a chain reaction resulting in the
aggregation
of
several
hemoglobin
molecules, which form a fibrous structure
that distorts the erythrocyte into a sickleshaped cell
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 In the R conformation of haemoglobin that
exists in the oxygenated state, the nonpolar
residues that bind to valine (β-6) are not
exposed on the surface, and aggregation of
haemoglobin molecules does not occur
 Deoxygenated haemoglobin exists in the T
conformation in which the nonpolar residues
that bind valine (β-6) are exposed on the
surface
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 Therefore, aggregation of haemoglobin
molecules and sickling of erythrocytes occur
when haemoglobin is present in the
deoxygenated form i.e. at low oxygen
tension
 Sickled erythrocytes are susceptible to
premature destruction
 Rapid destruction of erythrocytes causes
haemolytic anaemia
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 Inheritance of sickle cell anaemia is autosomal
recessive
 If the defect is inherited from one parent only, it
results in sickle cell trait which doesn’t cause any
clinical abnormality
 If the defect is inherited from both the parents, it
results in sickle cell disease and sever
haemolytic anaemia
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 It has been shown that the presence of
haemoglobin S gives some protection against
malaria
 The malarial parasite inhabiting erythrocytes gets
killed when the erythrocytes are destroyed
 Prevalence of haemoglobin S has been found to
be higher in those areas where malaria is
endemic
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Haemoglobin M
 This is also known as haemoglobin Boston
 It is formed when the histidine residue at position
58 in the α chain is replaced by tyrosine due to a
point mutation
 Bonding of phenol group of tyrosine with iron
converts the ferrous form of iron into the ferric
form (methaemoglobin) which cannot combine
with oxygen
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Thalassaemia
 This results from a decrease in, or lack of,
synthesis of either α chains or β chains
 Defective synthesis of α chains leads to αThalassaemia and that of β chains leads to
β - Thalassaemia
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A variety of genetic defects are
known to cause
Thalassaemia e.g.
 Deletion of a part or whole of a gene
 • Defective processing of the primary
transcript
 • Defective transport or translation of mRNA
 • Premature termination etc
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 Decreased synthesis or lack of synthesis of
one type of chain leads to an overproduction
of the unaffected chain
 This results in the formation of a
haemoglobin having only α chains or only β
chains
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 When the defect is transmitted by only one
parent, it results in Thalassaemia minor
which is symptomless
 When the defect is transmitted by both the
parents, it results in thalassaemia major
which is associated with severe anaemia
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MYOGLOBIN
 John Kendrew in 1960 (NP 1962) elucidated
the structure of myoglobin.
 It is seen in muscles.
 Myoglobin content of skeletal muscles is 2.5
g/ 100 g; of cardiac muscle is 1.4 g % and
smooth muscles is 0.3 g%.
 Mb is a single polypeptide chain.
MYOGLOBIN
 Mb have higher affinity to
Hb.
o
o2 than that of
 The p 2 in tissue is about 30 mm of Hg,
when Mb is 90 % saturated.
 The isoelectric point of Mb is 6.5.