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Chemistry and Functions of
Hemoproteins
Chemistry And Functions Of
Hemoglobin and Myoglobin
Synopsis
What are Hemoproteins?
What is Hemoglobin?
Structure of Hemoglobin
Functions of Hemoglobin
ODC and Factors affecting it
Normal Hb Variants
Hemoglobin Derivatives
INTRODUCTION
Hemoproteins
What Are Hemoproteins?
Hemoproteins are
Conjugated Proteins
With Heme as a
Prosthetic group in
their structures.
Hemoproteins are
Globular Proteins
(Whose Axial ratio less than 10)
Examples Of
HEME CONTAINING
PROTEINS AND ENZYMES
Of Human Body
Human Body Hemoproteins
Compounds with Heme group
Heme Containing Proteins
1. Hemoglobin (Hb)
2. Myoglobin (Mb)
3. Cytochromes (ETC Components)
Heme Containing Enzymes
1. Catalase
2. Peroxidase
3. Tryptophan Dioxygenase/
Tryptophan Pyrrolase
Hemoproteins are
vital for human body
Study Of Hemoglobin
What Is Hemoglobin?
Hemoglobin(Hb)
is a major
Hemoprotein of
Human body.
Hemoglobin Chemically is:
Conjugated Protein
In Hemoglobin
Heme is a Prosthetic group
Globin is a Protein part
(Hemoglobin = Heme + Globin)
Hemoglobin(Hb) is Red color
pigment
Location Of Hemoglobin-
Inside Red blood cells/Erythrocytes
of blood.
Amount Of Hemoglobin-
oEach RBC has approx
250-300 million Hb
molecules
oIn 25 x 1012 Erythrocytes
-750 gm of Hb
Hemoglobin In RBCs
Occupies:
33% of the RBC volume (1/3)
90-95% of the dry weight of
RBC is by Hb.
Normal concentration of
Hemoglobin in the Human Blood:
Adult Males-
13.5?17.5 gm/dL
Adult Females-
12.5?16.5 gm/dL
Hemoglobin Biosynthesis-
6.25 gm/day is the amount of Hb
biosynthesized during stages of
Erythropoiesis in bone marrow.
Synthesis of Hb begins in
Proerythroblast:
65% at Erythroblast stage
35% at Reticulocyte stage
Hemoglobin Function
Hb is associated to Respiration
Mechanism
Hb is a characteristic of Aerobic
life very important for survival.
Hb brings exchange of Gases-:
O2 and CO2
Terminologies of Hemoglobin
Hemoprotein -Heme is a prosthetic group
Chromoprotein - Red in color
Metalloprotein - Metal Iron (Fe) present
Respiratory Protein- Connected to
Respiration process and Respiratory
Chain(Electron Transport Chain)
Oxygen Binding Protein-Binds with
molecular Oxygen and transports it.
HISTORICAL ASPECTS
Of
Hemoglobin
Hemoglobin due to its
red color, has been of
interest since antiquity.
? Hemoglobin was a :
? First Protein to be crystallized -
1849.
? First Protein whose Mass
accurately measured.
? Mol weight of Hb-67,000
Daltons.
?First proteins to have X-ray
Diffraction structure
determined.
?First protein to be studied by
Ultracentrifugation.
?First protein to show that a
point mutation can cause
problems.
STRUCTURE OF HEMOGLOBIN
Two parts of Hemoglobin
Heme-Prosthetic group
Globin-Protein part
Hemoglobin Structural y
Tetrameric-contain 4 subunits.
Quaternary level of structural
organization.
Allosteric, Complex, Compact
Spheroidal= 64 x 55 x 50
Globular Protein
vHb of adults (Hb A) is a
Tetramer with
v4 Polypeptide subunits /4
Globin subunits
vConsisting of 2 - and 2 -
Globin chains
Each Subunit of Hemoglobin
contains:
1 Globin Chain and 1 Heme
group with a central Fe2+ ion
(Ferrous ion)
Hemoglobin Structure
Heme
One Hemoglobin molecule- 4 Subunits
One Subunit- 1 Polypeptide
Globin chain and 1 Heme moiety
Four Subunits- 4 Globin
Polypeptide chains+ 4 Heme
moieties.
1 Heme binds with 1 Oxygen molecule
4 Heme binds with 4 Oxygen molecule
1 OxyHb = 4 Globin+4Heme+4Oxygen
In Hb 4 polypeptide
chains are visualized as
two identical dimers,
()1 and ()2.
Two dimers are linked to
each other by weak polar
bonds- movement at the
interface of these two occurs
more freely.
Two polypeptide chains within a
dimer are held together tightly
by:
Ionic bonds and Hydrophobic
interactions, which prevent their
movement relative to each other.
v Thus Hb with
Quartenary structure is
in native conformation.
Significance of 4 Hb Subunits
11 and 2 2:
confirms stability of the
molecule.
1 2 and 2 1 :
confirms solubility of the
molecule.
1 2 and 1 2:
permit oxygenation and
deoxygenation.
v a2-b2 or a1-b1 interface has
35 amino acid residues
contact.
v a1-b2 and a2-b1 have 19
amino acid residue
contact.
Hemoglobin has
Outer relatively Hydrophillic
surface (Composed of polar a.a
/Provides Solubility)
Interior Hydrophobic (Made of
non polar a.a /insoluble a .a- Influences
Folding)
STRUCTURE /CHEMISTRY
OF HEME
Chem icWha
ally t
He I
m se H
is e
a me?
Ferroprotoporphyrin.
Prosthetic group of Hemoproteins
Red color pigment
Located interiorly in hydrophobic
Heme pocket present in Globin
subunit of Hb.
Metalloporphyrin
Chemically Heme is a
Ferroprotoporphyrin.
Heme Is- Ferroprotophoryin-IX
Protoporphyrin IX ring + Ferrous (Fe++)
Structure Of Heme
Structure Of Protoporphyrin IX-
Cyclic substituted Tetrapyrrole ring
structure (I,II,III and IV Tetrapyrrole ).
Tetrapyrrole rings has substituted
groups in systematic manner-
MV,MV,MP,PM
(M=Methyl ,V=Vinyl, P=Propionyl)
In Protoporphyrin ring ,Four
substituted Pyrrole rings are linked
by- 4 Methenyl bridges
Planar network of conjugated
double bonds of Heme absorbs
visible light and give red color
to Heme.
Structure of Heme
Iron in Heme
Functional form Iron in
Heme is-
Ferrous form(Fe++)
Reduced state
Fe++ located centrally
in Protoporphyrin ring
system.
Fe of Heme is
Hexavalent.
Fe of Heme forms 6 coordinated
bonds to satisfy its six valencies:
4 bonds linked with each Nitrogen
of 4 Pyrrole rings.
5th bond linked with Proximal
Histidine (F8) of Globin chain
( Globin=87, Globin=92).
6th bond is with Oxygen.
Binding of Iron in Hemoglobin-
Fe ++ is bound to :
4 Nitrogen of
Protoporphyrin ring
Globin chain ( Nitrogen of
Proximal His)
Oxygen
Iron content of Hb -
3.4 mg / gm of Hb
Role Of Iron in Hemoglobin
The Mineral, Iron, plays
indirectly an important
role in the body's
Delivery and use of
Oxygen by working
Muscles.
Iron helps in binding
Oxygen to Hemoglobin,
Oxygen get bound to Hb
then travels in the blood
stream to reach each and
every cell of the body.
Required amount of
Oxygen, delivery to
cells
Increases the body's
ability to perform
work.
Iron supports Aerobic Exercise
It has been postulated that a lack
of Iron in the body :
Reduces Aerobic capacity
Impair endurance
performance of exercise.
Iron of Heme gives red color
The visible absorption
spectra for Hemoglobin
The red color arises
from the differences
between the energy
levels of the d
orbitals around the
Ferrous atom.
Dietary Iron Deficiency
Features of Iron
deficient red blood
cells
Low number of
red blood cells
Hollow and
blanched red
cells
Iron deficiency is related to
Iron Deficiency Anemia
Low dietary Iron
Low Heme and Hb formation
Low Oxygen transport and release at
tissues and cells
Low cellular respiration
Low ETC operation in cells
Low ATP production in cells
Low cellular activity
Structure of Globin
Globin Subunits
Adult Hemoglobin has 4
Polypeptide chains
2 and 2 (identical pair).
Alpha Globin chains-
Composition- 141 amino acids
Molecular. Wt = 15,126 Daltons
Biosynthesis-Expression of
Globin gene on 16th Chromosome.
Beta Globin chains-
Composition- 146 amino acids
Molecular. Wt =15,866 Daltons
Biosynthesis- Expression of
Globin gene on 11th chromosome.
In Hemoglobin ?
2 (282 amino acid residues)
2 (292 amino acid residues)
Total 574 amino acids are
present in 1 Hemoglobin
molecule.
Each linear Globin
Polypeptide chain folds
To form 3 dimensional
Tertiary structure subunit.
Polypeptide chain has 8
Helices named as A, B, C, ...H.
Heme Pocket
Heme Pocket is a crevice/
hollow hydrophobic area
Formed in the interior of
Globin subunits
To locate the Heme moiety
in it.
The Heme pocket is surrounded
by E , F and H helices but not
with A , B, C ,D and G.
Heme group is tucked between
E and F helices of Globin subunit.
Amino acids in Globin chain are
identified by
The helix name and position
of a.a in that helix.
E7 His ( Distal His)
F8 His ( Proximal His)
Distal Histidine-E7 ( 58 , 63)
Proximal Histidine -F8 ( 87 , 92)
Fe++ of Heme is linked to
Proximal Histidine (F8)
O2 is linked to Distal
Histidine(E7).
Proximal and Distal His are
present in Heme pocket
In which Heme residue lies
and facilitates Oxygen binding.
Linking of Divalent O2 :
1.
Fe++ of Heme
2.
Nitrogen of Imidazole
group of Distal Histidine
of Globin chain( 58, 63)
Thus to attain stability
Oxygen is bound to
both Heme and Globin .
FUNCTIONS OF HEMOGLOBIN
Hemoglobin has important role in
Respiration mechanism-
v Hb Majorly Transports-
Oxygen (97% -100%)
v Hb Minorly Transports ?
Carbon dioxide (15% -25 %)
vDeoxy Hemoglobin
Transports-Protons(H+)
vThis is also termed as
Haldane effect
Hemoglobin Plays Role as Buffer-
(Hb/Hb-H+) in the Erythrocytes
Resists change in pH
Imidazole group of amino acid
Histidine of Hb molecule ?
Participates in buffering
mechanism of Hb.
Role Of Hemoglobin in Respiration
Since Hemoglobin has important role
in respiration mechanism, it is termed
as Respiratory Protein.
Respiratory Protein Hb serves in
transport and exchange of gases (O2
and CO2) between lungs and tissues.
How Significant Is
The Presence of Hemoglobin
To Human Body?
Why Natural y
There Is Presence
Of Hemoglobin
In the Living Bodies?
Presence of Hb in
blood
Gives less load to
Heart
Body cells requires approx. 500
gm/day of molecular Oxygen.
Molecular Oxygen is sparingly
soluble in body fluids.
This limits the Oxygen
transport in blood < 30 gm /day.
In fact if the body had to
depend upon dissolved
Oxygen in the plasma to
supply Oxygen to the cells.
The Heart would have to
pump 140 liters per minute.
Instead of normally 4 liters
per minute.
Hemoglobin a Polar, Oxygen
binding Protein/Oxygen
carrying Protein of blood.
Increases the binding and
effective transportation of
Oxygen through blood.
Presence of Hb in blood
facilitates the blood
To dissolve approx 70 times
more Oxygen than the plasma
without Hb can do.
oTotal Hb present in
each RBC
oCarry approx. More
than 1 billion Oxygen
molecules.
Thus to accomplish the following functions
Red blood cells has Hemoglobin (Hb):
Transfer of O2 from lungs to tissue
Transfer of CO2 from tissue to lungs
Hemoglobin serve as a
vehicle for transporting
the Oxygen
Through blood to reach
each and every cell.
Oxygen transported by Hb and
reached to every cell is used up in
Mitochondrial ETC
(Respiratory Chain/Cellular
respiration)
To generate ATP
(Oxidative Phosphorylation)
SALIENT FEATURES
OF
OXYGENATION
AND
DEOXYGENATION
OF HEMOGLOBIN
Oxygenation/Loading of
Oxygen
Hemoglobin gets Oxygenated
At Lungs
At increased pO2 concentration
(100-120 mm Hg)
At decreased pCO2
Saturation Of Oxygen By Hb
Normal ranges of pO2
100-120 mm Hg in arterial
blood at Lungs
35-40 mm Hg in venous
blood at tissues.
Hemoglobin is 97 % saturated
with Oxygen when it leaves the
Lungs-(Arterial Blood-Oxy Hb).
Under resting conditions Hb is
about 75% saturated with
Oxygen when it returns-(Venous
blood- Deoxy Hb).
Pulse Oximeter Is An
Instrument
That Measures The Percentage Hb
Ful y Saturated With Oxygen In
Arterial Blood
Thus the degree of
saturation with Oxygen is
related to:
Oxygen tension (pO2)
Oxygen requirement for
metabolic use at cellular
level
Features of Oxygenation of Hb
Oxygen binds with Hb to form HbO2
Oxygen links to Ferrous form
of Iron, of Heme
Non enzymatically, loosely
and reversibly.
During oxygenation One Hb
molecule with 4 Heme can
bind to four O2 molecules.
Binding of Oxygen to Heme of
Hb subunits:
Is weakly at low pO2
Is tightly at high pO2
Rate Of Hb Oxygenation:
? Less than 0.01 sec is required
for Hb Oxygenation.
?During Oxygenation
Ferrous of Heme is not
oxidized to Ferric.
v Oxygenation of
Hemoglobin causes
vConsiderable structural
conformational change
in Globin subunits.
Binding of Oxygen to Hb
rearranges the electronic
distribution and alters the d
orbital energy.
This causes a difference in
the absorption spectra.
Bluish for Deoxy Hb
Reddish for Oxy Hb
Measuring the absorption
at 578 nm allows an easy
method to determine the
percent of Oxygen bound to
Hemoglobin.
Ferric form of Iron is
non functional form
and cant bind with
Oxygen.
Deoxygenation/Unloading or
Offloading of Oxygen
Hemoglobin gets Deoxygenated
At Tissues
With Increased pCO2
Decreased pO2 levels (40 mm Hg)
? Deoxy Hb has 2,3-Bis Phospho
Glycerate (23BPG) within it located
central y
? 2,3-BPG is pushed out of the Deoxy Hb
molecule during oxygenation
? Globin chains move closer when Hb
is Oxygenated.
Globin chains are pulled apart
when Hb is deoxygenated
This permits entry of 2,3-BPG
resulting in unloading of Oxygen
When Hb is fully
saturated with Oxygen
Each gram of
Hemoglobin is bound
with 1.34 ml of Oxygen.
COOPERATIVE BINDING
MECHANISM OF OXYGEN WITH
HEMOGLOBIN
Oxygen Binds To Hemoglobin
with
Cooperative Mechanism
Positive Al osteric Effect
Of Hemoglobin
Hb is an Allosteric Oxygen
binder with cooperative
mechanism.
Cooperative binding mechanism
is due to Tetrameric structure of
Hb.
Oxygen binding at the
four sites to the Heme
of Hemoglobin does not
happen simultaneously.
The binding of the first O2
to one subunit of Hb.
Enhances the binding of
futher O2 molecules to
remaining subunits of Hb
with greater affinities.
When Oxygen binds effectively
with one subunit
There increases the Oxygen
affinities for remaining
adjacent subunits, this is called
positive cooperativity.
Fourth Oxygen
molecule binds to fourth
subunit of Hb
300 times rapidly and
tightly as that of first
Oxygen bound to first
subunit.
Thus Hemoglobin is a
remarkable molecular
machine
That uses motion and
small structural changes
to regulate this action.
When a First Oxygen binds to Fe
in Heme of Hb,
The Heme Fe is drawn into the
plane of the Porphyrin ring.
This initiates a series of small
conformational changes that are
transmitted to adjacent Globin
subunits.
Oxygen ligand binding
information is
transmitted from one
subunit of Hb to another.
During Deoxygenation
Hemoglobin releases its bound
Oxygen.
As soon as the first Oxygen
molecule drops off, the
Hemoglobin starts changing its
shape.
This prompts the
remaining three Oxygen
molecules to be quickly
released.
In this positive
cooperative way
Hemoglobin picks up the
largest possible load of
Oxygen in the lungs,
And delivers the Oxygen
where and when needed.
T AND R FORMS
OF Hemoglobin
During loading and unloading
of Oxygen by Hb there occurs
considerable amount of
Allosteric movement.
This is due to the Oligomeric
/Tetrameric Structure of the
Hb molecule.
Models for Al osteric Behavior
Monod, Wyman, Changeux (MWC)
Model:
Allosteric Proteins can exist in two
states:
v R (Relaxed) State ? Oxy Hb
v T (Taut/Tensed) ? Deoxy Hb
Oxy & Deoxyhemoglobin
Quaternary structure of
Deoxy and Oxy Hemoglobin
T-state
R-state
The conformation of the Deoxy
state of Hb is called the T state
The conformation of the Oxy
state of Hb is called the R
state
T form of Hb
Deoxygenated Hemoglobin
is T form or Tensed/Taut
form of Hemoglobin
conformation.
T form /Tensed/Taut form of Hb has:
Centrally 2,3 BPG
Hydrogen instead of Oxygen
CO2
(Illustration Man with Three Tasks)
These moieties are held together by:
Eight salt bridges/ non covalent
interactions.
Thus T form is more constrained
form.
T form
predominates in
the absence of O2.
T form has lower
affinity for
Oxygen in low
pO2 environment.
At the center in T form of
Hb there occupies 2,3BPG
molecule which stabilizes
the Deoxy state of Hb.
Hb has more affinity for 2,3
BPG when pO2 is low.
Hence R form(OxyHb) at
low pO2
Gets attracted towards 2,3
BPG
Binds with it and looses its
Oxygen at Tissues.
R form of Hb
Oxygenated Hemoglobin
is a R form or relaxed
form of Hemoglobin
conformation.
During Oxygenation salt
bridges of T form are broken
T conformation is transformed
to R form.
R form is less constrained.
R form has
higher affinity for
Oxygen in high
pO2 environment.
At the Lungs where pO2 is
high
T form(Deoxy Hb) has now
higher affinity for O2, than 2,3
BPG
Hence T form binds with
Oxygen, extruding 2,3BPG
and get transformed to R
Form.
In R form of Hb
Only Oxygen is bound
R form has No linkage of
2,3BPG molecule
Protons
CO2
T R
Hb + pO2 HbO2
Deoxy-Hb Lungs Oxy-Hb
Increase of partial
pressure of Oxygen (pO2)
Causes the conversion of
T-form to R-form of Hb.
Transformation Of
T to R form of Hb is at Lungs
R to T form of Hb is at Tissues
Directly depends upon pO2
concentrations in the
environment of body and cells.
The conformational
changes of Hb from T to R
form and vice a versa are
known as "Respiratory
movement".
O2 binds much tighter to R
than to T.
R form of Hb(OxyHb) is more
negatively charged.
T-form (Tense/Taut)
has a much lower
oxygen affinity than
the R-form.
Oxy versus Deoxy Hemoglobin
Oxygenation
rotates the a1b1
dimer in
relation to a2b2
dimer about 15?
T Form of Hb
R Form Of Hb
Deoxy Hb is in T form
Oxy Hb is in R form binds
binds with CO2,H+ and
only with Oxygen
2,3BPG
T form has 8 salt bridges
Salt bridges are broken in
linked in between the dimer between the dimer subunits
subunits
during oxygenation of Hb.
More constrained form
Less constrained form
2,3 BPG is centrally located 2,3 BPG is extruded out from
in T form of Hb
R form of Hb
T form has low affinity for R form has higher affinity
Oxygen
for Oxygen
T form of Hb predominates R form of Hb predominates
in low pO2
at high pO2
Il ustration
Lungs ? Class Room
Tissues/Cells? House Environment
Oxygen- Study/Knowledge
Hemoglobin- Student
pO2 ?Teacher
Increased pO2- Knowledgeable and Skilled Teacher
Decreased pO2-Poor knowledge and Skill
T form of Hb- Student at House with
Dance,Sport,Internet
R form of Hb- Student at Class Room with Study
Oxygenation- Grasping of Knowledge
Deoxygenation- Revision /practice of Knowledge
Metabolic Condition-Examination
Significance of Tetrameric
Al osteric Structure
Hb being Tetrameric,
Allosteric protein facilitates
Cooperative binding
mechanism of Oxygen.
Enhances the efficiency of
Hb as an Oxygen transporter
Hb rapidly bind with oxygen
in lungs where pO2 is high (100
mm Hg)
Hb liberate Oxygen at tissue
capillaries where pO2 is low
(40mm Hg)
4 Factors Affecting
(Al osteric Effectors)
Loading and Unloading of Oxygen
At Lungs and Tissues
1. pO2 Concentration
2. pCO2 Concentration
3. pH (H+ Ion Concentration)
4. 2,3
BisPhosphoGlycerate
(2,3BPG/2,3DPG)
5. Glucose Concentration
6. Metabolic Condition
pO2 Concentration
At lungs pO2 concentration is
high pO2 =100-120 mmHg /torr
This favors oxygenation and
loading of oxygen by DeoxyHb.
DeoxyHb (T form) transformed to
form OxyHb (R form).
At Tissues pO2 concentration is low
35-40 mmHg /torr
This favors deoxygenation and
unloading of oxygen by OxyHb
OxyHb(R form) transformed to form
Deoxyhb (T form).
pCO2 And pH
At tissues due to active
metabolism
There is high
concentration of pCO2
and H+ ion concentration
(Low pH values).
Increased pCO2 and low pH at
tissues
Favors the OxyHb to loose
affinity for Oxygen,
Which in turn help in
unloading/off loading of oxygen
at tissues
(R form changes to T form).
The Bohr's Effect
Relation of Hemoglobin between
pCO2, pO2 and pH
Described by Danish Physiologist
Christian Bohr In 1904
The Bohr effect is a
physiological phenomenon
which states that:
Hemoglobin's Oxygen binding
affinity is inversely related for
both acidity and
concentration of Carbon
dioxide.
Thus The effect of
pCO2 and pH on
OxyHb is known as
Bohr's effect.
Bohr effect facilitates release of
Oxygen/Unloading Of Oxygen.
Since the tissues are relatively rich
in Carbon dioxide, the pH is
lower than in arterial blood;
Bohr effect is a
manifestation of
The acid-base equilibrium
of Hemoglobin.
CO2 + H2O CA H2CO3 CA H+ + HCO3-
Hydration of CO2 in tissues and
extremities leads to Proton production.
These Protons are taken up by Hb after
Oxygen released at tissues to Lungs.
The Protons transported by Hb are
released at the lungs.
Binding of protons to
Hb diminishes Oxygen
binding to Hb.
Binding of Oxygen to
Hb diminishes Proton
binding to Hb.
As the Proton(H+)
concentration increases
Affinity of Hemoglobin
towards Oxygen is
reduced.
At acidic pH (More H+ ion
concentration)-Favors unloading
of Oxygen from OxyHb
At alkaline pH(Less H+ ion
concentration)-Favors loading of
oxygen to Deoxyhb.
At lungs low pCO2 and low H+.
Favors oxygenation or loading of Hb
by O2.
Deoxyhb transports H+(protons)
from tissues to lungs.
On oxygenation of Deoxyhb, the
protons are liberated at lungs.
Effect Of 2,3BPG
on Loading and Offloading
Of Oxygen by Hb
2,3 Bis Phospho Glycerate
2,3 Bis Phospho Glycerate
(2,3BPG/2,3DPG) is an
intermediate of Rapaport
Leubering cycle
Related to Glycolysis inside
mature Erythrocytes.
2,3BPG is impermeable
to RBC membrane.
Glucose metabolism in
Erythrocytes increases the
concentration of 2,3BPG.
The "Inside" Story......
Where does 2,3-BPG bind ?
"Inside"
In the central cavity of Hb molecule.
What is special about 2,3-BPG ?
Negative charges interact with 2 Lys, 4
His, 2 N-termini of Globin.
At low pO2, 2,3BPG has high
affinity for adult Hb.
Increased 2,3BPG levels ?favors
Oxygen unloading by Hb.
Decreased 2,3BPG levels -favors
Oxygen loading by Hb.
The T form of Hb has 2,3
BPG centrally located
Which lowers the affinity
for Oxygen.
As the partial pressure of Oxygen
increases(pO2),
The 2,3, BPG is extruded out, and the
Hemoglobin resumes its original
state, known as the "Relaxed" or "R"
form,
R form has a high affinity for
Oxygen.
Conditions Of
High levels of 2,3BPG
During conditions of
cellular deprivation of
Oxygen.
2,3BPG levels in
Erythrocytes are increased
Conditions Of
High levels of 2,3BPG
Hypoxia
At high Altitudes
Severe Anemia
Lung Diseases
Cardiac disease -Anoxia
Blood loss
2,3 BPG levels in Hypoxia
2,3BPG levels increases in
hypoxia and at high altitudes.
Changes in 2,3-BPG levels
play an important role in
adaptation to hypoxia.
In hypoxic conditions pO2 is low
and
2,3 BPG levels are high
Due to affected metabolism of
Glucose in RBC's.
Increased 2,3-BPG levels
in red cells
Decreases Oxygen affinity
Facilitates unloading of
Oxygen to tissues.
Increased 2,3-BPG
also plays a role in
adaptation to
exercise.
Conditions of
Low 2,3BPG levels
Prolonged starvation
Erythrocyte disorders reduces
the levels of 2.3BPG.
Low 2,3 BPG reduces low
unloading of oxygen at tissue
level.
However formation of 2,3-BPG is
not very essential to life.
An individual who lacked the
enzymes necessary for 2,3-BPG
synthesis (Rapaport Leubering )
was perfectly well except for mild
Polycythemia.
The increased Oxygen
affinity of stored blood is
accounted (Blood Banks)
Due to reduced levels of
2,3-BPG.
Inosine addition to
stored blood in blood
bank
Increases the 2,3BPG
levels in it
This favors unloading
Oxygen on blood
transfusion.
OXYGEN DISSOCIATION CURVE
OF HEMOGLOBIN
(ODC)
Oxygen Dissociation Curve
(ODC) of Hemoglobin
ODC describes the relation
between
Partial pressure of Oxygen
(pO2) and percent saturation
of Oxygen by Hb.
ODC for Tetrameric ,Al osteric
Hb molecule is sigmoid shaped
(S shaped)
Sigmoid Shaped ODC Curve
Due To
Positive Allosteric Effect
Cooperative Binding Mechanism
Of Oxygen With Hb
p50 Of ODC
P5o is that pO2 value
Where the Hb is 50
percent saturated
with Oxygen.
P50 is 50% saturation
of Hb at pO2 of 27
mm Hg.
In ODC of Hb
P50 for Adult Hb
is 27 mm.Hg/torr
ODC depicts
O2 carrying
capacity of Hb
at different pO2
Salient Features Of ODC of Hb
Oxygen Dissociation
Curve Depicts:
Oxygen uptake and
release by Hemoglobin.
ODC Describes
The fractional saturation
of Heme groups of
Hemoglobin with Oxygen
at various Oxygen partial
pressures.
Normally the partial O2 pressure in the
Lungs is 100 mm.Hg and the Hb is
100 % saturated with O2.
In Tissues the partial oxygen pressure is
40mm.Hg and the Hb is 75% saturated
with O2.
100 - 75 = 25% of the O2 is released by
OxyHb and delivered to the tissues.
Percent Saturation Of Hb
At Different pO2
pO2 in torr
Percent Saturation
Of Hb
100 in Alveoli
97 %
40 in resting muscles
64 ? 75 %
20 in working muscles
20%
10 in vigorously exercising
10%
muscles
The sigmoid shape of the ODC curve
shows that:
With a small drop in partial O2
tension (pO2).
A significant amount of O2
release/offloading by OxyHb will
occur.
It is to be noted that the
OxyHb reaching to
tissues
Does not releases its
Oxygen completely at
one instance.
Instead the release of
Oxygen by OxyHb at
tissues is
As per the cellular need
for the Oxygen .
This regulated way of Oxygen
release by OxyHb at tissue level
May prevent from generation of
oxygen derived free radicals
(Reactive Oxygen Species: ROS)
Which in turn protect the
peroxidation of cellular
biomolecules by action of ROS.
FACTORS AFFECTING ODC
OR
ALLOSTERIC MODULATORS of ODC
The characteristics of normal
ODC depends upon following
factors:
Hemoglobin Structure
Environment within the
Erythrocyte
The environment Of
RBCs depends upon:
pO2
pCO2
pH(H+ concentration)
2,3-Bisphosphoglycerate
Glucose Concentration
Metabolic Condition
Temperature
Increased
H+,pCO2, 2,3BPG,Temperature
Causes unloading of Oxygen
from OxyHb.
They are Negative Allosteric
effectors of ODC.
Types And Conditions
Of ODC Shifts
Right Shift of ODC
With Its Conditions
If the Oxygen Dissociation
Curve is shifted towards Right
v Oxygen is unloaded by OxyHb
Oxygen affinity is decreased by Hb
Oxygen is not linked and
not retained in the Hb structure
Conditions Which Shift ODC
To
Right Hand Side
Low Oxygen Affinity/Easy Oxygen Delivery/Easy
Unloading/ Prompt Offloading of Oxygen
? High pCO2 (Increased Metabolic States)
? High H+ (Acidosis)
? High 2,3-BPG: Hypoxic , Anoxic Conditions
? Exercise
? High body temperature : (Fever)
? Anemia : Hb S (low pO2)
Mnemonic for Factors causing
Right Shift of ODC :
CADET
C ? CO2
A ? Acid (H+)
D? 2,3-BPG /2,3 DPG
E ? Exercise
T ? Temperature
Left Shift of ODC
With Its Conditions
If the Oxygen Dissociation
Curve is shifted towards Left
Oxygen is not unloaded by OxyHb
Oxygen affinity is increased by Hb
Oxygen is linked and
retained in the Hb structure
Conditions Which Shift ODC
To
Left Hand Side
High affinity for Oxygen/ Low oxygen
Delivery/poor unloading of Oxygen
? High pO2
? In Alkalosis ( Low H+ high HCO3-)
? Low 2,3-BPG
? HbF
? Increased Methb and Carboxyhb
COMPARISON OF AN O2 DISSOCIATION CURVE AT NORMAL PH
AND WITH ACIDOSIS OR ALKALOSIS
Transport Of CO2 and H+
About 75 - 80% of tissue
Carbon dioxide is
processed and
transported in the form
of HCO -3(Bicarbonate ions)
Carbon dioxide
formed during
metabolism in tissues
is out in plasma
Then it diffuses freely
into the Erythrocytes
In aqueous solutions,
carbon dioxide undergoes a
pair of reactions
biocatalyzed by enzyme
Carbonic Anhydrase (CA).
Reaction 1
CO + H O H CO (Carbonic Acid)
2
2
2
3
Reaction 2
H CO H+ + HCO - (Bicarbonate ions)
2
3
3
Where the presence
of an enzyme
Carbonic
Anhydrase facilitates
reaction 1.
The H+ liberated in
reaction 2 are accepted by
deoxygenated
Hemoglobin, and
transported
The bicarbonate formed
in this sequence of reactions
Diffuses freely across the
red cell membrane and a
portion is exchanged with
plasma Cl-,
A phenomenon called the
"Chloride shift."
The bicarbonate ions are
carried in plasma to the
lungs
Where excretion of CO
2
occurs in the expired air.
Hb Minorly Transports CO2
15 ? 20% of CO2 is
Transported by Hb.
Transport of Carbon
dioxide by Hb, is unlike
that of Oxygen
CO2 does not bind to
Heme/Fe++ of Hb
CO2 is linked to
Globin part of Hb
and transported.
CO2 is bound to the
To Deoxygenated Hemoglobin
In Globin chains
At N-terminal Amino groups of
Valine residue
To form Carbaminohemoglobin
2 molecules of CO2 are
linked to 1 Hemoglobin
Transported through
blood from tissues to
Lungs and expired out.
? 5% of CO2 is
carried in free,
dissolved form
through blood.
Thus Deoxy Hb
carries:
CO2 and Protons
from Tissues to
Lungs.
At Lungs as Oxygen
gets bound to Deoxyhb
The CO2 and H+ comes
off of Deoxyhb and
expired out of Lungs.
At Lungs
At Tissue level
Respired air ?
Metabolism
pO2 is high ?90-100 mm Hg
pO2 is low-40mm Hg
pCO2 is high.
pH low (H+ high),2,3BPG high.
Hb is oxygenated to OxyHb (R Form)
OxyHb is dissociated to release
Cooperative binding mechanism of O2 to
oxygen at tissue level./O2 is
Hb
unloaded. OxyHb is deoxygenated
`T' form is transformed to `R' form.
R form is transformed to T form.
O2 binds to Fe ++ of Heme non
O2 released by Hb at tissue level is
enzymatically loosely and reversibly.
utilized for Biological Oxidation
and process(ETC).
4 O2 to 1 Hb
15-25% of Co2 is transported to
1.34 ml O2/gm of Hb transported
lungs by Hb forming
Carbaminohemoglobin and expired
out through lungs.
O2 is directly linked to Fe ++ of Heme and
CO2 is not linked to Fe ++ of Heme
distal His of 58 a.a and 63 a.a of Globin. But linked to amino groups of Val
residue.of Globin subunits
NORMAL HB VARIANTS
Normal Hb variants are
type of Hemoglobins
Present in different
physiological phases of
human life.
Role of Normal Hb Variant
:
To rightly fit for that
particular physiological
phase of life
Transport and Deliver
Oxygen as per need and
maintains normal cellular
activity.
Examples of Normal Hb Variants
Of Human Body
Globin Chain Synthesis,
starts at 3rd week of gestation.
Embryonic Stage/Embryonic
Hb -
vHemoglobin Gower I (z2e2)
vHemoglobin Gower II (a2e2)
vHemoglobin Portland (z2g2)
Fetal Stage:
v Major Hb : Hb F (a2g2)
v Minor Hb :HbA1(a2b2)
Adult Stage:
v Major Hb : Hb A1 (a2 b2)
v Minor Hb :
vHb A2 ( a2 d2)
vHb A3 (In old RBC's)
vHb F (a2 g2)
vGlycosylated Hb/Hb A1c
All Globin polypeptide chains are
homologous which arise from same
ancestral Genes.
Beta Polypeptide chain-146 a.a
Gamma chain-146 a.a
(differ in 39 a.a from chain )
Delta chain -146 a.a
(differ in 10 a.a from chain)
GLOBIN GENES
Of
Normal Hb Variants
Globin Gene Clusters
GLOBIN CHAINS In
Different Stages Of
Human life
Globin chain switch
Fetal Hemoglobin
(HbF)
HbF is a normal Hb
variant of fetal life
Hb F Predominates:
Fetus
New born infants
Fetal Hb (Hb F)
Globin part has : 2 and 2 subunits.
Globin chain differs
from Globin chain
in 39 amino acid
residues
Histidine residue at 143
position of Globin chain of
Hb A is replaced with
Serine a neutral amino
acid In Hb F .
Biosynthesis Of Hb F
Expression of following Globin genes
will produce and Globin chains
to form HbF:
Globin Gene located on 16 Chromosome
Globin Gene located on 11 Chromosome
Hb F biosynthesis starts by
7th week of gestation.
In Fetus Hb F predominates
during
Second and Third trimester
of gestation
At birth in newborn infants.
After birth there is rapid post
natal decline in HbF levels.
Within 4 months after birth
HbF is almost completely
replaced by Hb A.
Globin chain switch
Function and Features
Of HbF
HbF functions in
loading and unloading
of Oxygen in Fetus and
new born infants.
Hb F has a high
affinity for O2 than
HbA1.
Hb F has low
affinity for 2,3 BPG
HbF binds with O2 at
lower pO2 concentrations
than Hb A1.
P 50 for Hb F is 20 torr.
HbF has low Oxygen
releasing/unloading
capacity.
Thus ODC for HbF is
shifted towards Left.
Significance Of Hb F in Fetal Stage
The fetus is circulated
with maternal blood
Which has
comparative low pO2
as that of Lungs.
Hb F having high
Oxygen affinity
Gets oxygenated at low
pO2 of maternal blood.
This makes more
efficient trans placental
transfer of Oxygen from
maternal blood to fetal
HbF.
Thus Hb F in fetal phase rightly
fits for this state:
Since there is a low metabolic
activities in fetal cells and
requirement of low Oxygen.
Thus low release of Oxygen by
HbF suffice in this condition.
High levels of Hb F
In Adults Is Abnormal
Normally HbF in adults is less
than 1 %
HbF more than 1% in adult
hood is abnormal.
15-20% of HbF is found in patients
of Sickle Cell disease.
(Defect in Globin Genes)
More higher percent of HbF
is noted in individuals
suffering from
Thalassemia.
(Defect in Globin synthesis)
High levels of HbF in Adults will
have low release of Oxygen at
tissue levels:
Where the metabolic state and
requirement of Oxygen is high.
Thus HbF does not fit in adult
life.
P50 values for Hb A and HbF
P50 for Hb A= 27 mm.Hg
P50 for Hb F= 20 mm.Hg
Adult Hemoglobins
Adult Hemoglobin Forms
Hb A1
Hb A2
Hb F
Globin chain a2b2
a2d2
a2g2
combinations
Normal %
96-98 %
1.5-3.2 %
0.5-0.8 %
Globin chain synthesis in adults
25% 25%
0.5% 1.5%
48%
25% 25%
0.5% 1.5% 48%
Chromosome 16
Chromosome 11
Hb A1
HbA1 is the major form
of Hb in adults and in
children over 7 months.
Globin has 2 and 2
subunits.
Hb A2
HbA2 has 2 and 2
Globin subunits.
Hb A2 is a minor form
of Hb in adults.
Hb A2 is 2 ? 3% of a total
adult Hb.
Hb A3
HbA3-altered form
of HbA1 found in
old RBC's.
Approx 3-10 %.
Hb A1
Hb F
P D
r iffe
edo
r
min eannc
t af etser be
1 yea tr w ofe Predominant in fetus and
birth and adults.
enn A
ew dult
born in - HbA
fants.
1
G and F
lobin ch e
a t
in al- HbF
-2 2
Globin chain-2 2
Less affinity towards O2 and More affinity towards O2
more affinity towards 2.3
and less affinity towards 2.3
BPG at tissues
BPG at tissues.
P50 is 27 mm.Hg
P5o 20 mm.Hg
Unloading power of oxygen Unloading power of oxygen
at tissue level is high.
at tissue level is low.
HbA1 denatured by alkali
Hb F resistant to alkali
denaturation.
ODC of Fetal Hb F vs. Adult Hb
GLYCOSYLATED
HEMOGLOBIN
(HbA1c)
Hb undergoes
spontaneous
glycosylation with
Glucose present in
Blood/RBCs.
The extent of glycosylation
with Hb depends on the
plasma concentration of
Glucose.
Once Hb is glycated
it remains till the
life span of RBC
(120 days).
Site Of Linkage Of Glucose
To Hemoglobin
Glucose is linked to Globin
part of Hemoglobin to Amino
acids:
Valine (terminal a.a ) of
Globin chain and
Lysine amino group
vLater the linked
Glucose is
transformed to
1-Deoxy Fructose.
Significance of Estimation
of
Blood Glycosylated Hemoglobin
Glycosylated Hb (HbA1c)
in normal healthy adults
is less than 5%
In Diabetes mellitus the
HbA1c is more than 5%
WHO Criteria for Diabetes Mellitus
HbA1c > 6.5%
Levels of Glycated Hb
gives idea of
Blood Glucose levels of a
person in last 3-4
months back.
Thus estimation of
Glycosylated Hb from blood
specimens in clinical
Biochemistry laboratory:
Gives Index of Glucose
Control in patients of known
Diabetes mellitus.
As the blood Glucose
levels increases
The percentage of
Glycosylated Hb increases
High Levels Of Glycosylated Hb
Decreases Oxygen Transport to
Tissues
Increased Glycosylated Hb
increases its affinity for
Oxygen.
Prevent release/unloading of
Oxygen at tissues
Induces hypoxia in extreme
cases
Increased Glycosylated Hb
Decreases Oxygen saturation
with Hb.
Increased Glycosylated Hb
Decreases Oxygen release at
tissues
Risk Of High Levels Of
Glycosylated Hb
In Patients Of Diabetes Mellitus
Diabetes mellitus Patients
Glycated hemoglobin of 6.5% -
Less risk for development of Diabetic
complications.
Glycated hemoglobin of 12 %-
High risk for development of Diabetic
complications.
HEMOGLOBIN DERIVATIVES
Hemoglobin interacts with chemical
agents to form Hb derivatives.
During formation of Hb derivatives
mostly Fe+2 part of Hb is involved.
Hemoglobin
O2
NORMAL HB DERIVATIVES
Normal Hb derivatives are
physiological and functional
forms of Hb.
Examples of Normal Hb derivatives.
OxyHb- Hb Bound to O2
Reduced Hb- Hb Bound to H+
ABNORMAL HB DERIVATIVES
or
Dyshemoglobins
Abnormal Hb Derivatives are
Acquired ones:
Abnormal Hb derivatives are
formed:
When blood interacts with
Chemical pollutants/Drugs
which has affinity for Hb.
Abnormal Hb derivatives has
Heme Iron linked to other
chemical compounds
instead of O2
OR
Hb is in a state where
Oxygen may not get linked
to Heme.
Examples of Abnormal Hb
Derivatives
1. Carboxyhemoglobin- CO linked to Fe+2 of Hb
2. Methemoglobin-Fe+2 of Heme transformed to
Fe+3
3. Cyanmethemoglobin-CN linked to Methb
4. Sulfhemoglobin-H2S interacted with Hb,
5. Sulfur linked to Fe +2 of Hb
6. Hematin- Ferriprotoporphyrin.
7. Hemin- Hematin Chloride.
8. Hemochromogen - Heme with denatured
Globin.
9. Cathemoglobin - Hematin with denatured
Globin.
Consequences of
Abnormal Hb Derivatives/
Dyshemoglobins
Dyshemoglobin Causes
Cyanosis
(Low Oxygen Saturation By Hb)
Dyshemoglobins in acquired states
affect normal structure and
function of Hb.
Dyshemoglobins are non
functional forms of Hb.
Dyshemoglobins affects Oxygen
transportation from lungs to
tissues.
CARBOXYHEMOGLOBIN
or
Carbon Monoxide Poisoning
Carbon Monoxide (CO)
is a colorless ,odorless,
toxic gas
Present in atmosphere as
chemical pollutant.
Sources of CO
Product of incomplete combustion of
fuel by vehicles.
Byproduct of Coal mines.
Cigarette Smoking (more than 4%).
Endogenous normal metabolism-
Heme catabolism(Heme Oxygenase
step)
CO has 200 times
more affinity for
Hb than O2.
CO readily links to Fe+2 of Hb and
form- Carboxyhb (Pink colour).
CarboxyHb has no place for binding
O2.
CarboxyHb reduces transportation
and delivery of O2 by Hb.
CarboxyHb delivers CO
at tissues instead of O2.
CO released in cells is
inhibitor of Cytochrome
oxidase in ETC.
CarboxyHb Toxicity
Toxicity due to CarboxyHb
is noted when concentration
is more than 20% in blood.
Concentration more than 40
-60% of Carboxyhb in body
may lead to death.
Symptoms of CarboxyHb Toxicity:
v Nausea
v Vomiting
v Headache
v Breathlessness
v Irritability
vFatigue
Investigation for CarboxyHb
Study of blood sample using
Hand Spectroscope.
Characteristic bands at 527
and 580 nm in green region
of visible spectrum confirms
presence of CarboxyHb.
Management and Treatment
Of CO Poisoning
Carbon monoxide poisoning
may be reverted
By increasing high
concentrations of O2
Cyanotic cases of Carboxyhb
treated by administration of
oxygen mask/Oxygen
cylinder.
Oxygen under high pressure
is helpful in managing
severe cases of CO toxicity.
Increased pO2 favors
replacement of CO by O2 to
form OxyHb transport and
deliver to tissues and support
the metabolic function.
METHEMOGLOBIN
Methemoglobin (MetHb) is an
abnormal Hemoglobin
derivative.
Methemoglobin has
Hematin/ Heme Iron in Ferric
(Fe+3) state.
Hematin is Ferriprotoporphyrin
Hematin +Globin = Methemoglobin
MetHb has defect in Heme
with normal Globin part.
MetHb has non functional
Iron- which cannot bind with
O2 and transport it.
Methemoglobin is non
functional oxidized
form of Hemoglobin.
Fe+3 of Hb gets
coordinated with water
instead of Oxygen at the
sixth position.
Formation of Methemoglobin
OR
Causes Of Methemoglobinemia
Normally about 1% of
Methemoglobin is
produced in blood
circulation.
Abnormal high levels of
blood Methemoglobin is-
Methemoglobinemia
Causes for Methemoglobinemia:
Acquired Cause :
Increases above 2% can
occur with the ingestion of
strong oxidant drugs
When blood is exposed to Oxidant Drugs
,Hb interacts with it and Fe+2 of Heme
truly gets oxidized to Fe+3.
Potassium Ferricyanide
Nitrites
Chlorates
Antipyrins
Sulfa Drugs (Sulfonamides)
Aniline Dyes
Conversion
Of
Methemoglobin
To
Hemoglobin
Reducing agents converts
Methemoglobin to functional Hb.
Glutathione
Ascorbic acid
Enzymes converts Methemoglobin
back to
Hemoglobin:
Methemoglobin Reductase
Cytochrome b5 Reductase
Conversion Of Methemoglobin To
Hemoglobin is
NADPH+H+ Dependent
H2O2 and Oxidant Drugs
Hemoglobin
Methemoglobin
(Fe+2)
(Fe+3)
Methemoglobin Reductase
NADP+ NADPH+ H+
The source of
NADPH+H+ for the use
of Methemoglobin
reductase activity is
Pentose Phosphate
Pathway(HMP Shunt).
Defect in HMP Shunt
affects the conversion of
Methemoglobin to
Hemoglobin due to devoid
of NADPH+H+
Congenital Causes of
Methemoglobinemia
As a result of deficiencies of
Methemoglobin
Reductase
G6PD enzyme of HMP
shunt
Familial Methemoglobinemia
Inherited deficiency of
Enzyme Methemoglobin
Reductase in the body
Causes Familial
Methemoglobinemia.
G6PD deficiency of HMP shunt
reduces generation of NADPH+H+
Which in turn affects
Methemoglobin Reductase
activity also leads to
Methemoglobinemia.
Methemoglobin Reductase in
absence of NADPH+H+
Does not convert
Methemoglobin back to
Hemoglobin.
Methemoglobin levels in blood
gradually increases to
Methemoglobinemia.
Consequences
Of
Methemoglobinemia
Methemoglobin is brown
colored pigment.
Hence
Methemoglobinemia ?
termed as :
Chocolate Cyanosis
Toxic Effects Of Methemoglobin
Methb has Fe+3 which is non
functional
Does not bind and transport
O2 to tissues.
Instead binds with water.
10-20% of Methemoglobin- Mild
Cyanosis.
50-60% of Methemoglobin- Severe
Cyanosis, Cardiopulmonary
Symptoms-Tachycardia, Depression.
More than 60% of Methemoglobin-
Unconsciousness and death.
Investigation Of MetHb
Study of Blood Sample
using Hand
Spectroscope.
Performing Schumm's
Test (Spectroscopy)
Management Of
Methemoglobinemia
Oral administration
of reducing agents
Ascorbic acid
Methylene Blue
Dried blood and old meat
have brown color.
Butchers uses Ascorbic acid
to reduce Methemoglobin to
make the meat look fresh!!
Sulfhemoglobin
Sulfhemoglobin - occurs when the
sulfur content of the blood
increases due to
Ingestion of sulfur containing
drugs
In chronic constipation( Gut
bacteria acts on unexcreted
material produces H2S)
Sulfhemoglobin is greenish
compound where sulfur is
covalently attached to
Porphyrin ring (Not to Iron).
Sulfhemoglobin cannot bind
with Oxygen.
Unlike the formation of
Carboxyhb and Methb,
The formation of Sulfhb is an
irreversible change of Hb.
Drugs producing Sulfhemoglobin:
Dapsone (Leprosy treating drug)
Phenacetin
Acetanilide
Sulfanilamides
These drugs produce Methb too
MYOGLOBIN
Myoglobin (Mb)-
Mb is a Hemoprotein of red
skeletal muscles.
Primarily occur in Cardiac
muscles.
Structure Of Myoglobin
Myoglobin is a
Monomeric unit
Mb is composed one
Globin chain and one
Heme moiety.
Myoglobin (Mb)
Mb is Spheroidal ,globular
molecule 44 x 44 x 25
Mb: Mol Wt 17,200 Daltons.
Myoglobin is rich in alpha
helix.
Globin part of Myoglobin is
composed of single
polypeptide chain
Composed of 153 amino
acid residues.
Myoglobin contains 1 Heme
group which binds with 1 O2 .
Iron in Mb is Fe2+ (Ferrous ion)
the functional form that binds
Oxygen.
Oxygen binds as the sixth
ligand to Fe (MbO2)
Myoglobin has very low
p50 value 2-3 torr/mm.Hg.
ODC of Myoglobin is
simple hyperbolic curve.
In comparison to Hemoglobin A and
HbF Myoglobin has high affinity for
Oxygen.
Hb F and Mb has low p50 values as
compared to p50 value of Hb A1.
With low p50 ,more Oxygen binds at
low pO2.
Function Of Myoglobin
Myoglobin is found in
cytosol of skeletal and
Heart muscles.
Myoglobin facilitates rapidly
Respiring muscle tissue
The rate of O2 diffusion from capillaries to
tissue is slow because of the solubility of
Oxygen.
Myoglobin increases the solubility of
Oxygen.
Myoglobin facilitates Oxygen diffusion.
Myoglobin in Muscle
Cells is a:
Oxygen storing
Hemoprotein
Reservoir of Oxygen
Myoglobin does not allow
Oxygen to remain in free state:
Oxygen diffused in muscle cells is
used up in Oxidative
phosphorylation.
If Oxygen remained unused in the
cells it immediately binds with Mb
to form MbO2
MbO2 releases/unloads
O2 when required.
MbO2 unloads oxygen
at extreme conditions
When pO2 of cellular
level reaches to 5 mm Hg.
Myoglobin releases
Oxygen in rapidly
respiring cells.
The released O2 is used
up in Oxidative
Phosphorylation.
Mb present within muscle cells comes
out in blood after damage to muscle
cells.
Mb is found abnormally in blood and
urine of MI cases.
Thus elevated Myoglobin levels in
blood/urine is a marker of
Myocardial damage.
Metmyoglobin does not
bind to Oxygen.
Since oxidation of Fe+2 yields
Fe +3 -Ferric iron
(non functional form)
Differentiate Between Hb and Mb
S.No Hemoglobin (Hb) Myoglobin (Mb)
1. Diffe
Hb rise
O nc
xyge e
n t s
ra nsof
port
Mb is Oxygen storing protein in
protein in RBCs of bloo Hb
d.
A
mu nd
scles. Mb
2.
Tetrameric has four Heme and Monomeric has one Heme and
binds with 4O2
binds with 1 O2.
3.
Oxygenated at Lungs
Oxygenated at Muscle Cell
Cytosol.
4.
HbO2 unloads oxygen at
MbO2 unloads oxygen at cell
tissues when pO2 is at 40
cytosol when pO2 is at 5 mmHg. To
mmHg.
rapidly respiring cells
P50 for HbA1 is 27 torr.
P50 for Mb is 2 torr.
5.
ODC is sigmoid shaped
ODC is hyperbolic shaped.
6.
Hb has 574 amino acids.
Mb has 153 amino acids.
Mol .wt-67,000 Daltons.
Mol wt-17,200 Daltons.
Cytochromes
Cytochromes ? Hemoprotein.
Cytochromes are components
of ETC
Who bring Oxidative
phosphorylation and
generates ATP .
Cytochrome P450-
Involved in Drug
detoxification.
Catalase and Peroxidases
Enzymes present richly in
Peroxisomes of cells.
Catalase and Peroxidase are of
Enzyme Class- Hydroperoxidases.
Glutathione
Peroxidase (R.B.C)
Leucocytes
Peroxidase (W.B.C)
Catalase and Peroxidase
Detoxify H2O2
Substrate for Catalase and
Peroxidase is H2O2 which detoxify
it.
Catalase and Peroxidase decomposes
2H2O2 to 2 H2O and O2.
Role of Catalase and Peroxidase
v Prevents accumulation of H2O2
(Toxic free radical) in cells .
vPrevents Peroxidation of membrane
lipids and protect cellular lysis.
Tryptophan Dioxygenase
Tryptophan Dioxygenase/Tryptophan
Pyrrolase involved in Tryptophan
catabolism.
Deficiency of Tryptophan Dioxygenase
Accumulates Tryptophan without its
breakdown to liberate Acetyl-CoA
(Ketogenic precursor) and Alanine
(Glucogenic precursor).
Deficiency of Tryptophan
Dioxygenase
Blocks Kynurenine
Pathway for the biosynthesis
of Niacin from Tryptophan.
Effect Of Cyanide and Carbon
Monoxide on Hemoproteins
CN and CO disrupts
physiological function of
HemoProteins.
Thus CN inhibits the function
of Hb ,Mb, Cytochromes.
Impaired activity of these
Hemoproteins
Badly affects Oxygen
metabolism and ATP
generation.
More affected cells are
Nervous system,
Erythrocytes.
Questions Of Hb Chemistry
1. Structure Of Hemoglobin
2. Heme Structure
3. Globin Structure
4. Functions of
Hemoglobin/Biomedical
Importance of Hemoglobin.
5. Salient features of Hemoglobin
Oxygenation and Deoxygenation.
6. Allosteric Effectors of Loading and
Unloading of Oxygen by Hemoglobin.
7. 2,3 BPG and its role in Hb.
8. ODC of Hemoglobin and factors
affecting it
9. CO2 Transportation in human body
10. Normal Hb Variants
11. Glycosylated Hb and its significance.
12. Hemoglobin Derivatives
13. Dyshemoglobins/Abnormal Hb
derivatives
14. CarboxyHemoglobin
15 . Methemoglobin
16. Types of Hemoproteins
Differentiate between following:
1. Hb A and Hb F
2. Hemoglobin and Myoglobin
3. T form and R form of Hb
4. Hb at Lungs and Hb at Tissues/
Oxygenation of Hb and
Deoxygenation of Hb.
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This post was last modified on 05 April 2022