chapter 7 hemoglobi portrait of a protein in action Flashcards
In which states can iron exist?
ferrous 2+ and ferric 3+
the functions of myobglobins
faciltate diffusion of oxygen through cells and a reserve supply of oxygen to be used when needed
why is the release of superoxides from myoglobin is dangerous
1- They are highly reactive species
2- they leave iron in the ferric state Fe 3+ cannot bind oxygen
the functions of the distal histidin
1- found in the binding pocket of myoglobins. donates a hydrogen bond to the bound oxygen stabilising the oxymyoglobin
2- May also impair access of CO to the heme group which has dire consequences
what does the protein component of myglobins do?
Controls the intrinsic reactivity of heme making it more suitable for reverisble binding
what happens to quarternary structure of hemoglobins upon oxygen binding
a1B1 rotates around 15 degrees with respect to a2B2
Models of hemoglobin cooperativity
1- concerted model
2-sequential model
The difference between the concerted model and sequential model
In concerted model, the tetramer can exist in only 2 states. Binding to the first subunit affects the whole tetramer.
In the concerted model. One affects the neighbouring one and not the whole tetramer
what structural change favours the T to R transition in hemoglobins
when iron moves into the plane of the porphyrin, the proximal histidin associated also moves closer to the porphyrin. This causes the carboxyl-terminal of the alpha-helix containing the proximal histidine to lie at the interface between the two aB-dimers
Thalassemia
caused by an imbalanced production of hemoglobin chains
why doesn’t excess alpha chain precipitate?
alpha hemoglobine stabilising protein. forms a soluble complex with monomeric alpha chains.binds to the same face of alpha helix as beta-subunits do. The complex formed is less stable than the alpha-beta formation. Therefore the alpha hemoglobin stabilising protein dissociates when B is present
