Biochemistry I Oxygen Transport
 
 

 Myoglobin and Hemoglobin
   Myoglobin
   Hb    a1  a2   b1  b2
   Highlight heme

 Heme
   Heme    Heme+His (myo)

 Oxygen binding to Hemoglobin
   Hb(a) - deoxy      Hb(a)-oxy 
   Hb(a)-oxy/deoxy     zoom
      
[Green = beta chain, purple & cyan = alpha chain, orange = helix F]

 BPG-site
   DeOx(a,b,BPG-site)   
   Ox   

Notes:
  1. Both myoglobin and hemoglobin are largely a helical.
  2. Both myoglobin and hemoglobin contain heme.
  3. The heme binding pocket is hydrophobic. Heme binds due to van der Waals and hydrophobic effects.
  4. Myoglobin is structurally homologous to each subunit of hemoglobin
  5. Oxygen binding displaces the distal His
  6. Oxygen binding 'pulls' the proximal His and its attached helix (F) towards the heme
  7. The displacement of helix-F causes conformational changes that are propagated to the other sub-units, increasing their affinity.
  8. BPG (bis-phosphoglycerate) binds in a charged cavity between two b sub-units in deoxy Hb. Oxygen does not bind here!
  9. The BPG binding cavity closes in oxy-hemoglobin, therefore BPG favours the deoxy state.