Types Of Hemoglobin

Types Of Hemoglobin

1. Normal Hemoglobin

   • Fetal hemoglobin (HbF)
     • Tetramer with two a and two g chains
     • Higher affinity for O2 than HbA
     • Transfers O2 from maternal to fetal circulation across placenta
   • HbA2
     • Appears ~12 weeks after birth
     • Constitutes ~2% of total Hb
     • Composed of two a and two d globin chains
   • HbA1c
     • HbA undergoes non-enzymatic glycosylation
     • Glycosylation depends on plasma glucose levels
     • HbA1c levels are high in patients with diabetes mellitus

2. Unable to transport O2 due to abnormal structure

   • Abnormal Hbs
   • Carboxy-Hb
     • CO replaces O2 and binds 200X tighter than O2 (in smokers)
   • Met-Hb
     • Contains oxidized Fe3+ (~2%) that cannot carry O2
   • Sulf-HB
     • Forms due to high sulfur levels in blood (irreversible reaction)

3. Hemoglobinopathies : Disorders of hemoglobin

   • caused by:
     • Synthesis of structurally abnormal Hb
     • Synthesis of insufficient quantities of normal Hb
     • Combination of both
   • Sickle cell (HbS) disease
     • Caused by a single mutation in b-globin gene
     • Glutamic acid at position 6 in HbA is replaced by valine
     • The mutant HbS contains bs chain
     • The shape of RBCs become sickled
     • Causes sickle cell anemia
   • Hemoglobin C disease
     • Caused by a single mutation in b-globin gene
     • Glutamic acid at position 6 in HbA is replaced by lysine
     • Causes a mild form of hemolytic anemia
   • Methemoglobinemia
     • Caused by oxidation of Hb to ferric (Fe3+) state
     • Methemoglobin cannot bind oxygen
     • Caused by certain drugs, reactive oxygen species and NADH-cytochrome b5 reductase deficiency
     • Chocolate cyanosis: brownish-blue color of the skin and blood
   • Thalassemia
     • Defective synthesis of either a or b-globin chain due to gene mutation
       • a-thalassemia
         • Synthesis of a-globin chain is decreased or absent
         • Causes mild to moderate hemolytic anemia
       • b-thalassemia
         • Synthesis of b-globin chain is decreased or absent
         • Causes severe anemia
         • Patients need regular blood transfusions

4. Immunoglobulins

5. Contains a single polypeptide chain forming a single subunit with eight a-helix structures

   • Myoglobin
     • diseases
       • Myoglobinuria
         • Myoglobin is excreted in urine due to muscle damage (rhabdomyolysis)
         • -May cause acute renal failure -Specific marker for muscle injury -Less specific marker for heart attack