CGIER 36 - Haemoproteins II: Co-operative oxygen binding to haemoglobin binding of CO2 and H+ Flashcards
oxygenation reaction
Hb + 4O2< —->Hb(O2)4
where does oxygenation occur and why
in lungs where there is a high concentration of haemoglobin
what are the conditions muscles are in
low O2 and pH from respiration
why would haemoglobin not have O2
when pH and O2 is low affinity of myoglobin for oxygen is greater than that of haemoglobin (see previous slide) and O2 is transferred from oxyhaemoglobin to myoglobin
respiration equation
C6H12O6 + 6O2 —>6 CO2 + 6 H2O
why is pH and O2 low in muscle
respiration occurs in muscles O2 is used to release CO2 which will make weak carbonic acid and water
H+ is also produced by metabolism in the muscle cells.
how is CO2 and H+ transported to the lungs
free haemoglobin in muscles bind to CO2 and H+ and transports it to the lungs
how does CO2 react in blood when CO2 is transported
Most CO2 produced in respiration reacts with water (catalysed by carbonic anhydrase) and is converted to bicarbonate (HCO3-) in erythrocytes
other ways in which CO2 react with blood in carbon dioxide transport
Some however reacts with haemoglobin and forms a carbamate (a carboxylic acid with an amino group directly
attached) - CO2 binds to N atom from amino group of haemoglobin
cooperative oxygen binding
Addition of the 1st O2 molecule to haemoglobin is difficultHowever when this happens the Fe(II) to which it binds changes from high-spin to low-spin The Fe(II) shrinks & moves out of porphyrin plane into it. proximal histidine along with globin chain moves salt linkages break haem groups are exposed and more relaxed strcuture allowing 3 more Oxygens in
describe structure particularly compactness of haemoglobin
Haemoglobin is a compact (tense) structure in which the globin chains interact by salt (electrostatic)
linkages.
allosteric proteins
An allosteric protein is one in which an interaction at one site in the molecule affects interactions at remote sites. e.g. haemoglobin NOT myoglobin
allosteric effects in haemoglobin
O2 binding at one site of haemoglobin helps binding of other O2 in remote sites of same molecule
Binding of H+ and CO2 at particular lead to charged groups being formed leads to formation of salt linkage - tense state - O2 removed
capillaries of alveoli of lungs binding of O2 in Hb causes breaking of salt bridges and release of CO2 and H+
Bohr Effect
The inter-relationship between H+, CO2 and O2
binding in haemoglobin
how is carbon monoxide made
when carbon is burned in insufficient Oxygen
describe gaas carbon monoxide
odourless colourless gas
where is carbon monoxide
exhaust fumes of cars mainly ones w/o catalytic converters, house fires, poorly maintained oil or gas heaters.
why is carbon monoxide toxic?
The affinity of haemoglobin for CO is 225 times greater than its affinity for O2
Affinity of myoglobin for CO is ~ 25 times greater than its affinity for O2
Binding to CO instead of O2 - respiration cannot occur and one can die
The binding is so strong it is regarded as irreversible
how could CO be more toxic
If the Fe-C≡O group was linear (thus more stable) and no H-bonding was involved the affinity of haemoglobin for C≡O would be 25,000 times greater than affinity for O2.
CO is more stable with histidine than with O2
how was the body engineered itself to make CO less toxic
Nature engineered a way to reduce stability of CO complex and increase stability of O2 complex.
explain the importance of distal histidine
The distal histidine which is located close to the O2 and CO binding site on the haem forces CO to bind at an angle
This destabilises the Hb(CO)4 complex.
distal histidine’s involvement in destabilising the Hb(CO)4 complex is an example of..
allosteric effect
how is oxygen stabilised in haem group
of strong H bonding between a partial negative charge on the non-bridging oxygen and the distal histidine.
which complex is distal histidine more responsible for stabilising oxyhaemoglobin or carbonmonoxyhaemoglobin
The distal histidine stabilises oxyhaemoglobin by hydrogen bonding – more than it does carbonmonoxyhaemoglobin
how is carbon monoxide poisoning treatment
CO poisoning is treated by administering pure O2 under high pressure (2 or 3 atm) in hyperbaric units
why is carbon monoxide poisoning treated by administerd pure O2 under high pressure
Under these conditions O2 dissolves in the plasma to a much higher degree than usual and tissues receive enough oxygen to recover.
how much exposure to O2 is dangerous and how does it affect the body
exposure to O2 at 2 atm for 6 hours causes damage to lung tissues and the central nervous system.
what is the recommended time and pressure of administering O2 to body
2 hrs at 2 atm or 1½ hrs at 3 atm
