Haemoglobin Flashcards
Purpose of Haemoglobin?
It overcomes low O2 by being a tetrameric haem protein found in erythrocytes and binds to oxygen. it returns CO2 to the lungs
What is Myoglobin?`
A monomeric haem protein which facilitates oxygen transport to rapidly repairing tissues. it recieves oxygen from Hb
What is Cooperative binding?
when the ligand changes with the amount of ligand already bound
Adult and Fetal Hb structure?
Adult Hb = a2b2
Fetal Hb = a2y2
How is Hb stabilised?
A heme group is incorporated into proteins during protein synthesis, stabilised by hydrophobic residues on the inside.
A protective environement prevents oxidation of Fe2+ so it can react with O2
What is the globin fold?
It is 8-alpha helices connected by loops. Heme binds between E and F, histidine residues from E and F are situated near the haem iron
Histidine in Hb?
Distal histidine stabilises O2 bound Hb and destabilised CO bound Hb, CO binds much stronger in Hb compared to free heme
When O2 binds to Hb, the iron centre moves into the plane of the haem and is stabilised by histidine
in absence of O2 the iron centre shifts below the plane of haem
Oxygen binding in Hb?
This induces Fe2+ and F-helix movement
Facilitates the allosteric transition from the T to R state
The Bohr effect?
Occurs in the peripheral tissues where there is low pH and so a decreased affinity for O2 so it is released
in the lungs, there is high pH, and so an increase for oxygen affinity.
The T-state and the R-state in the lungs?
In the lungs the Hb shifts to the R-state, changing His back to normal pKa, as pH lowers, pronation of His occurs
CO2 reacts with Hb’s N-termini producing carbamino Hb allowing for salt bridges to stabilise the T-state
T-state has less O2 affinity, R-state has more
The physiology of BPG?
increasing the BPG concentration pushes the oxygen dissociation curve frim higher to lower affinity as O2 is harder to bind, it prevents tissue hypoxia
BPG binds only during the T-state
