Hemoglobin Vs Myoglobin Flashcards
What is the role of hemoglobin
-oxygen transport
-heterotetramer: 2 alpha, 2 beta
subunits (tetramer)
-moderate affinity for O2
-sensitive to pH, [CO2] and [BPG] * binds 4 O2 molecules
What is the role of myoglobin
-oxygen storage protein
-monomer
-High affinity for 02
-Unaffected by PH, [CO2],[2-3-bpg]
-Binds 1 O2 molecule
How does myoglobin bind to O2
-binds to oxygen via a permanently bound cofactor/prosthetic group heme (aka haem)
-heme binds O2 via the Fe2+ ion
What are the strucutal changes of hemoglobin upon O2 binding
-induces a T- to-R state transition
-the R (oxy) state has increased affinity for O2 - so binding of O2 at 2 subunits increases the affinity of the other subunits for O2
-T state- Deoxy, low O2 affinity
-R-state- Oxy, high O2, affinity
what type of binding curve does myoglobin have?
Hyperbolic curve
what type of binding curve does hemoglobin have?
Sigmoidal curve due to cooperative binding
why does hemoglobin bind O2 cooperatively
-binding is very efficient since it permits full saturation of the protein in the lungs (or gills), where pO2 is high and efficient O2 release in tissues, where pO2 is low
what does cooperative mean
means that hemoglobin has a high affinity for O2 at high pO2 in the lungs and a low affinity for O2 in the low pO2 of the tissues
what would happen if O2 binding is not cooperative
O2 would either bind well at high pO2 but not release well at low pO2 or vice versa
What are the affects of BPG on hemoglobin oxygen affinity
2,3-BPG binding traps hemoglobin in the T state by interacting with numerous residues in the center of the hemoglobin tetramer
-binding of 2,3-BPG to a secondary site inhibits binding of O2 to the primary sites
How does low PH helps to unload oxygen in tissue
The low pH helps to protonate b1 His146, stabilizing the T state and favoring release of any remaining bound O2.
- increasing the pH (removing protons) stimulates Hb to bind more O2 at low pO2.
