Hemoglobin and myoglobin are oxygen-carrying proteins in the blood. Hemoglobin is a tetrameric protein composed of four polypeptide chains that carry oxygen from the lungs to tissues and carbon dioxide from tissues back to the lungs. Myoglobin is a single-chain protein that stores oxygen in muscle tissues. Both proteins use heme groups containing iron to reversibly bind oxygen. The binding of oxygen is influenced by factors like pH, carbon dioxide levels, and 2,3-bisphosphoglycerate to facilitate oxygen delivery to tissues and carbon dioxide removal from tissues.

1. HAEMOGLOBIN &
MYOGLOBIN
STRUCTURE

2. HAEMOGLOBIN
• Normal level of haemoglobin
14-16 g/dl (males)
13-15 g/dl (females)
• Globular in shape
• Molecular weight is 67,000 Daltons
• is conjugated protein containing globin –apoprotein and
heme - non-protein part
• Tetrameric allosteric protein
• Globin consists of four polypeptide chains of two different
primary structures
• Adult haemoglobulin (HbA) has 2 alpha chains and 2 beta
chains

3. Alpha & beta chains

4. Hb A Hb A2 Hb F
structure a2b2 a2d2 a2g2
Normal % 96-98 % 1.5-3.2 % 0.5-0.8 %
Adult haemoblobin

5. • Hb F (fetal Hb) is made up of 2 alpha and 2 gamma
chains, Hb A2 has 2 alpha and 2 delta chains
• Normal adult blood contains 97% HbA, about 2%
HbA2 and about 1% HbF
• Alpha chain gene is on chromosome 16 while beta,
gamma and delta chains are in chromosome 11
• Each alpha chain has 141 aminoacids residue and
beta, gamma and delta chains have 146 aminoacids
• Alpha and beta subunits are connected by relatively
weak non-covalent bonds
• Other varieties are Embryonic Hb , Glycosylated Hb

6. • There are 4 heme residues per Hb
molecules, one for each subunit in
Hb. The 4 heme groups account for
about 4% of the whole mass of Hb.
The heme is located in a
hydrophobic cleft of globin chain.
• Heme contains a porphyrin
molecule namely protoporphyrin IX,
with iron at its center
• Heme is common prosthetic group
present in cytochromes, in certain
enzymes such as catalase,
tryptophan pyrolase, and
chlorophyll

7. Function of Haemoglobin
Haemoglobin performs two important biological
functions concerned with respiration
Delivery of O2 from the lungs to the tissues
Transport of CO2 and protons from tissues to
lungs for excretion

8. (R)
relaxed state
(T)
tense state
The Transportation of Blood Oxygen
Hemoglobin
Lung
O2
Myoglobin
Muscle
Vein
Artery
When environmental [O2]
increases, Hb binds oxygen
efficiently
When environmental [O2]
decreases, Hb releases
oxygen to Mb
Any one subunit receives an oxygen molecule will increase the
oxygen-binding affinity of the others
Juang RH (2004) BCbasics

9. Combination of haemoglobin with gas
• Oxy-Haemoglobin
• Oxygenation not oxidation
• One Hb can bind to four O2 molecules
• Less than .01 sec required for oxygenation
• b chain move closer when oxygenated
• When oxygenated 2,3-BPG is pushed out
• b chains are pulled apart when O2 is unloaded,
permitting entry of 2,3-BPG resulting in lower affinity of
O2

10. Oxy & deoxyhaemoglobin

11. • Carboxy-Hb
– CO combines with heme portion of Hb
– Affinity of Hb to CO is 210 times more
than O2
– Lethal action due to inhibition of
cytochrome oxidase
• Combination with CO2
– Hb combine with CO2 to form
carbaminohaemoglobin
– Combination on globin rather than with
heme

12. • Sulfhaemoglobin
– Formed by the action of H2S on oxy-Hb
• Action with cyanide
– Cyanides do not react directly with haemoglobin
but they react with methaemoglobin to form
cyanmethaemoglobin which is not toxic

13. Abnormal haemoglobin
• Two types
• Mutation affects on structural gene
– E.g. HbS, HbM, HbC, HbD and others
• Mutation affects the regulator gene
– E.g. α-chain thalassaemias and β-chain
thalassaemias

14. MYOGLOBIN
• Myoglobin content of skeletal muscle is 2.5
g/100g; of cardiac muscle is 1.4 g% and of
smooth muscles 0.3 g%
• Mb is a single polypeptide chain, contains 152
aminoacids with a molecular weight of 17500
Daltons
• One molecule of Mb can combine with 1
molecule of oxygen

15. • Myoglobin functions as a reservoir for oxygen
• Also serves as oxygen carrier that promotes
the transport of oxygen to the rapidly
respiring muscle cells

16. Binding of O2 to haemoglobin
• Oxygen dissociation curve: the binding ability of
hemoglobin with O2 at different partial pressures
of oxygen (pO2) is shown by the oxygen
dissociation curve
• In pulmonary alveoli, Hb is 97% saturated with
oxygen where pO2 is 100 mmHg and in tissue
capillaries, where pO2 is 40 mmHg,theoretically,
Hb saturation is 75% but practically about 60%
saturated. So physiologically, 40% of oxygen is
released

17. 0 20 40 60 80 100 120
100
80
60
40
20
0
Percent
O
2
saturation
Partial pressure of oxygen (pO2, mmHg)
Muscle in
exercising
Relaxing
muscle Myoglobin
Hemoglobin
Artery
[O2]
Vein
[O2]
Environmental Oxygen Effects Binding Affinity
Adapted
from
Garrett
&
Grisham
(1999)
Biochemistry
(2e)
p.480

18. • The sigmoid shape of the oxygen dissociation
curve is due to the allosteric effect or
cooperativity
• The binding of oxygen to one heme residue
increases the affinity of remaining heme
residues for oxygen
• Each successive addition of O2 increases the
affinity of Hb to oxygen synergistically

19. • The quaternary structure of oxy-Hb is
described as R (relaxed) form; and that of
deoxy-Hb is T (tight) form
• These two forms are interconvertible and each
form has its own equilibrium constant (KR &
KT) for binding of O2

20. Hb-oxygen dissociation curve

21. • The normal position of curve depends on
• Concentration of 2,3-BPG
• H+ ion concentration (pH)
• CO2 in red blood cells
• Structure of Hb
Hb-oxygen dissociation curve

22. • Right shift (easy oxygen delivery)
• High 2,3-BPG
• High H+
• High CO2
• HbS
• Left shift (give up oxygen less readily)
• Low 2,3-BPG
• HbF
Hb-oxygen dissociation curve

23. BOHR EFFECT
• The binding of oxygen to hemoglobin
decreases with increasing H+ concentration or
when the hemoglobin is exposed to
increased partial pressure of CO2
• Bohr effect causes a shift in the oxygen
dissociation curve to the right
• Bohr effect is primarily responsible for the
release of O2 from the oxyhemoglobin to the
tissue

24. • Any increase in protons and/or lower pO2 shifts the
equilibrium to the right to produce
deoxyhemoglobin as happens in the tissues
• When CO2 binds to hemoglobin, carbamyl
hemoglobin is produced which causes the removal
of protons from the terminal NH2 group and
stabilizes the structure of Hb in the T form.

26. Haldane effect
• The carbon dioxide
equilibrium curve is nearly a
straight-line function of
PCO2 in the normal arterial
CO2 range
• The higher PO2 will shift the
curve downward and to the
right (Haldane effect)
• Its advantage is that it
allows the blood to load
more CO2 in the tissues and
unload more CO2 in the
lungs