Hemoglobin structure

3. Haemoglobin
• haemoglobin is a tetramer
• haemoglobin is the oxygen binding protein of
red blood cells and is a globular protein.
• haemoglobin consists of four polypeptide
subunits; 2 α chains and 2 non α

4. Introduction
• The main function of red blood cell
Gas transport protein
• Transfer of O2 from lungs to tissue
• Transfer of CO2 from tissue to lungs
• To accomplish this function red cells has haemoglobin (Hb)
• Each red cell has 640 million molecules of Hb
• HbA: 2 α & 2 β with heme .
• Molecular weight :68000 or 64500 daltons
• Other haemoglobin :HbF & HbA2

5. Normally Found Hemoglobin
Adult Hb (Hb A) 2 α and 2 β subunits
•HbA1 is the major form of Hb in adults and in
children over 7 months.
•HbA2 (2 α, 2 δ) is a minor form of Hb in adults.
It forms only 2 – 3% of a total Hb A.
Fetal Hb (Hb F) = 2 α and 2 γ subunits
in fetus and newborn infant,
After birth, Hb F is replaced by Hb A during the
first few months of life.

6. Hb AHb A Hb AHb A22 Hb FHb F
structurestructure 22ββ22 2222 22γγ22
Normal %Normal % 96-98 %96-98 % 1.5-3.2 %1.5-3.2 % 0.5-0.8 %0.5-0.8 %
Adult haemoblobin

7. haemoglobin
• Is a haemoprotein only found in the cytoplasm of
erythrocytes (ery)
Normal concentration of Hb in the
blood:
adult males 13.5 – 17.5 g/dL
adult females 12 – 15 g/dL

8. haemoglobin
• Blood can carry very
little oxygen in solution.
• haemoglobin is required
to carry oxygen around.
• haemoglobin is found in
red blood cells

9. haemoglobin
• Each red cell has 640
million molecules of Hb
• haemoglobin is 97%
saturated when it leaves
the lungs
• Under resting conditions
it is about 75%
saturated when it
returns.

10. haemoglobin
• haemoglobin is made from two similar
proteins that "stick together".
• Both proteins must be present for the
haemoglobin to pick up and release oxygen
normally.
• One of the component proteins is called α, the
other is β.

11. Haemoglobin
• Blood cells are made up of two components.
• The haemoglobin is inside the cell.
• The cell is surrounded by a membrane that
holds in the haemoglobin.

12. Structure of haemoglobin
Tetramer:
Haemoglobin is a tetramer composed of four Polypeptide chain
and four heme groups.
α chain consist of 141 Amino acids
β chains has 146 Amino acids
Helical :
Each polypeptide chain arrange in a helical structure.
There are eight helical segments designated A to H
Iron of heme is covalently bounds to histamine at Position F on
H Segment.

13. Heme
• Heme is suspended
in a pocket form by
the folding of the
poly peptide chain.
• The four Polypeptide
chain make contact
at α1β1 and α1β2

14. Iron and haemoglobin
• Iron, plays an important
role in the body’s
delivery and use of
oxygen to and by
working muscles.
• It binds oxygen to
haemoglobin, which
then travels in the
bloodstream to
locations throughout
the body.

16. Function of haemoglobin
Hb is a buffer (Hb/Hb-H+
) in the
erythrocytes
Hb is a carrier of O2 and CO2
Binding of O2is a cooperative. Hb binds O2
weakly at low oxygen pressures and tightly at
high pressures. The binding of the first O2 to Hb
enhances the binding futher O2 molecules →
allosteric effect → S-shaped (sigmoidal)
saturation curve of Hb

17. assignment

18. assignment
• methaemoglobin • Carboxy hb
• Nitroso hb myogloboin

19. Myoglobin (Mb)
• is a single-chain
globular protein of
153 AA, containing
1 heme group
• transports O2 in
skeletal and heart
muscle
• is found in cytosol
within cells
• is a marker of
myocard damage

20. Process of O2
binding to Hb
•Hb can exist in 2 different forms: T-form and R-form.
•T-form (T = „tense“) has a much lower oxygen affinity than
the R-form. The subunits of Hb are held together by electrostatic
interactions. The binding of the first O2molecule to subunit of the
T-form leads to a local conformational change that weakens the
association between the subunits → R-form („relaxed“) of Hb.
•Increasing of oxygen partial pressure causes the conversion
of T-form to R-form.

21. PROCESS OF O2
BINDING TO HB
• haemoglobin is a remarkable molecular
machine that uses motion and small structural
changes to regulate its action.
• Oxygen binding at the four heme sites in
haemoglobin does not happen
simultaneously.
• Once the first heme binds oxygen, it
introduces small changes in the structure of
the corresponding protein chain.

22. PROCESS OF O2
BINDING TO HB
• These changes nudge the neighboring chains
into a different shape, making them bind
oxygen more easily.
• Thus, it is difficult to add the first oxygen
molecule, but binding the second, third and
fourth oxygen molecules gets progressively
easier and easier.
• This provides a great advantage in
haemoglobin function.

23. PROCESS OF O2
BINDING TO HB
• When blood is in the lungs, where oxygen is
plenty, oxygen easily binds to the first subunit
and then quickly fills up the remaining ones.
• Then, as blood circulates through the body,
the oxygen level drops while that of carbon
dioxide increases.

24. PROCESS OF O2
BINDING TO HB
• In this environment, haemoglobin releases its
bound oxygen. As soon as the first oxygen
molecule drops off, the protein starts changing its
shape.
• This prompts the remaining three oxygens to be
quickly released.
• In this way, haemoglobin picks up the largest
possible load of oxygen in the lungs, and delivers
all of it where and when needed.

25. haemoglobin
The heme group of one subunit, shown in the little
circular window, is kept in one place so that you can see
how the protein moves around it when oxygen binds.
As it binds to the iron atom in the center of the heme, it
pulls a histidine amino acid upwards on the bottom side
of the heme.
This shifts the position of an entire α helix, This motion is
propagated throughout the protein chain and on to the
other chains, ultimately causing the large rocking
motion of the two subunits

26. Haem synthesis
• Haem consis of proporphyrin ring with an iron
atom at its center .The porphyrin ring consist
of four pyrole group,which are united by
methene =c= bridges.

27. Structure of Haeme

28. Haem synthesis
• Haem is synthesized from precursor succinyl
CoA and glycine,which condensed to Delta
Amino Laevulinic acid.dALA in presence of
ALA synthetase and pyrodixal phosphate as co
enzymes.

30. Factors affecting Oxygen Affinity
(Students assignement)
Temperature
pH
2 ,3 DPG

31. Derivatives of haemoglobin
 Oxyhaemoglobin (oxyHb) = Hb with O2
 Deoxyhaemoglobin (deoxyHb) = Hb without O2
 Methaemoglobin (metHb) contains Fe3+
instead of Fe2+
in heme groups
 Carbonylhaemoglobin (HbCO) – CO binds to Fe2+
in heme in case of
CO poisoning or smoking. CO has 200x higher affinity to Fe2+
than O2.
 Carbaminohaemoglobin (HbCO2) - CO2 is non-covalently bound to globin
chain of Hb. HbCO2 transports CO2 in blood (about 23%).
 Glycohaemoglobin (HbA1c) is formed spontaneously by nonenzymatic
reaction with Glc. People with DM have more HbA1c than normal (› 7%).
Measurement of blood HbA1c is useful to get info about long-term
control of glycemia.

32. Mutations in haemoglobin (haemoglobinopathies:
1- Sickle cell anemia (Hb S disease):
It is a genetic disorder of blood caused by mutation in β-globin
chain resulting in the formation of Hb S. The mutation occurs in 6th
position of β-chain where glutamic acid is replaced by valine .

33. Such sickled cells frequently block flow of blood in narrow
capillaries and block blood supply to tissue (tissue anoxia)
causing pain and cell death.
Note: The lifetime of erythrocyte in sickle cell is less than 20
days, compared to 120 days for normal RBCs.
Patients may be :
Heterozygotes (Hb AS): mutation occurs only in one β-
globin chain. These patients have sickle cell trait with no
clinical symptoms and can have normal life span.
Homozygotes (Hb SS): mutation occurs in both β-globin
chain with apparent anemia and its symptoms

34. 2- Hb C disease:
Like HbS, Hb C is a mutant Hb in which
glutamic acid in 6th
position of β-chain is
replaced by lysine.
RBCs will be large oblong and hexagonal.
The heterozygous form (HbAC) is
asymptomatic.
The homozygous form (Hb CC) causes anemia,
tissue anoxia and severe pain.