1- Is one of the most studied proteins in the body because of the ability to
easily isolate it from red blood cells (RBCs)
- 95% of cytoplasmic content of RBCs
Hemoglobin
21 Produced in the anaerobic glycolytic pathway (Luebering-Rapoport
pathway)
2 Bonded in the center of beta chains
3 Inversely related to the hemoglobin-oxygen affinity
2,3-Biphosphoglycerate (2,3-BPG)
3Heme Structure
- Also called as “Ferroprotoporphyrin IX”
4Heme consists of
1 Protoporphyrin IX
- ring of carbon, hydrogen, and nitrogen atom
2 Central atom of divalent ferrous iron (Fe22+)
- reduced iron
5- metabolically active iron
- binds oxygen
- used for heme synthesis
Ferrous Iron/ Reduced Iron (Fe2+)
6- transported by transferrin
- stored form of iron (ferritin or hemosiderin)
Ferric Iron/ Oxidized Iron (Fe3+)
8Chromosome 11
Beta
Delta
Epsilon
Gamma
9HEME BIOSYNTHESIS
1. Succinyl CoA = Glycine
2. Delta Aminolevulinic Acid (D-ALA)
3. Porphobilinogen
4. Hydroxymethylbilane
5. Uroporphyrimogen III
6. Coproporphyrinogen III
7. Protoporphyrinogen IX
8. Protoporphyrin IX
9. Heme
10HEMOGLOBIN ASSEMBLY
1. Heterodimer
2. tetrameter
3. four hemes and four polypeptide chains are assembled
4. Eight helices - egg shaped molecule with central cavity
5. change in the overall configuration of the hemoglobin molecule occurs
6. additional binding of oxygen to the remaining heme groups
11- Present up to the 3rd month of fetal life
Embryonic Hemoglobin
12- Predominant during the 2nd and 3rd trimester of fetal life and at birth (up to
6th month)
Fetal Hemoglobin
13- Predominant by the 6th month of age until adulthood with small amounts of HgBA2
Adult Hemoglobin (HgBA1)
14- Genetic abnormalities in the Hgb molecule
• 350 HgB variants
Hemoglobin variants
15- Are used for fractionation, presumptive identification, and quantification of
normal hemoglobins and hemoglobin variants
Hemoglobin Electrophoresis and HPLC
16Function of hemoglobin
High Oxygen Affinity
-To readily bind oxygen molecule to the lungs
Low Oxygen Affinity
-Transport oxygen
-To efficiently unload oxygen to the lungs
17Partial Pressure of Oxygen
- the amount of oxygen needed to saturate 50% of HgB, called the P50 value
Normal Value 24 mm/Hg
Shift to the left <27 mm/Hg
Shift to the right >27 mm/Hg
18The curve is sigmoidal, indicates
1) low HgB affinity for oxygen at low oxygen tension
2) high HgB affinity for oxygen at high oxygen tension
LEFT → increased affinity to HgB → Oxygen is NOT DELIVERED
RIGHT → decreased affinity to HgB → oxygen is DELIVERED
19P50 is the partial pressure of oxygen needed for 50% O2
saturation of HgB
Normal HgB-oxygen dissociation curve
20o 2,3-BPG
o Raised pH
o Partial pressure of carbon dioxide
o Temperature
Left-shifted curve with reduced P50 can be caused by decreases
21o HgB F
o HgB variants that have increased oxygen affinity
Left-shifted curve is also seen
22o 2,3-BPG
o Lowered pH
o Partial pressure of carbon dioxide
o Temperature
Right-shifted curve with increased P50 can be caused by elevations
23o HgB variants that have decreased oxygen affinity
Right-shifted curve is also seen
24FACTORS AFFECTING THE CURVE
1 Concentration of 2,3-biphosphoglycerate (2,3-BPG)
2 Body Temperature
3 Blood pH → Bohr Effect
4 Carbon dioxide → Haldane Effect
5 Fetal Hemoglobin → causes left shift
6 Abnormal Hemoglobin Variants → causes left shift
25Oxygenated or Relaxed State
-Oxygen is not released to the tissues (curve to the left)
Oxyhemoglobin
26Deoxygenated or Tense State
-Oxygen is released to the tissues (curve to the right)
Deoxyhemoglobin
27- Dysfunctional HgB that are unable to transport oxygen
-form and may accumulate to toxic levels, after exposure to
certain drugs or environmental chemical or gasses
Dyshemoglobin
28TYPES OF DYSHEMOGLOBIN
1 Methemoglobin
2 Sulfhemoglobin
3 Carboxyhemoglobin
29- Is formed by the reversible oxidation of heme iron to the ferric state
(Fe3+)
-cannot carry oxygen
Methemoglobin (MetHB or Hi)
-Increased methemoglobin = decreased delivery of oxygen in the tissues
30TOXIC LEVELS
<25% - Asymptomatic
>30%:
Cyanosis – bluish discoloration of the skin and mucous membrane
Hypoxia – dyspnea, headache, vertigo, change in mental status
>50% Coma and death
31- occurs in normal individuals after exposure to an
exogenous oxidant, such as:
1) Nitrite
2) Primaquine
3) Dapsone
4) Benzocaine
Toxic Methemoglobinemia
32Toxic Methemoglobinemia Treatment:
1) Removal of offending oxidant
2) >30% is treated with methylene blue or exchange
transfusions
33Mutations in the gene for NADH-cytochrome b5 reductase 3
(CYB5R3)
Methemoglobin - Hereditary
34Methemoglobin - Hereditary
• Autosomal recessive
• <50% of total hemoglobin
Cytochrome b5 Reductase Deficiency
35Formed by the addition of a sulfur atom to the pyrrole ring of heme
• In vitro and in the presence of oxygen, HgB reacts with hydrogen
sulfide
Sulfhemoglobin (HgBS)
Color of blood → Greenish pigment
Mauve-Lavender → sulfhemoglobinemia
36Sulfhemoglobin (HgBS) Causes:
1 Drugs (such as sulfanilamides, phenacetin, nitrites, and
phenylhydrazine)
2 Exposure to sulfur chemicals
3 Patients with severe constipation, in cases of bacteremia due to
Clostridium perfringens and Clostridium welchii
37results from the combination of carbon monoxide (CO) with heme iron.
• The affinity of carbon monoxide for hemoglobin is 210-240 times that
of oxygen.
Carboxyhemoglobin (HgBCO)
38Exogenous carbon monoxide is derived from the:
1) exhaust of automobiles
2) tobacco smoke → in smokers, HgBCO levels may be as high as
15% (higher HCT and Polycythemia to compensate for hypoxia)
3) industrial pollutants (such as coal, gas, and charcoal burning)
39Carboxyhemoglobin may be detected by:
spectral absorption instruments at 540 nm
40A diagnosis of carbon monoxide poisoning is made if the:
HgBCO level is:
o greater than 3% in nonsmokers
o greater than 10% in smokers