Module 3
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What does immunoglubilin consist of and how are they bonded to each other
4 sub units, 2 heavy chains and 2 light chains, interchain disulfide bonds
Why does antibodies evolved to be multivalent
Due to avidity
Why has hemoglobin evolved to be mltimeric
Because it exhibits allosteric
What is allosteric
regulation of an enzyme by binding an effector molecule at a site other than enzyme’s active site
what is multivalent
Having several sites at which attechment to an antibody or antigen can occur
What is multimeric
Having multiple polypeptide chains
What is the saturation of myoglobin and hemoglobin in comparison
myoglobin has higher affinity with O2 at lower pressure that exhibits a hyperbolic curve while hemoglobine have a lower affinity with O2 at a lower pressure which exhibits a sigmoidal curve
What are the two functions of Mb
storage of oxygen in muscles, it can release oxygen when rapidly contracting muscle
Where does the oxygen bind to in Mb
Binds to Fe2+ of the heme prosthetic group
What is oxygen in Mb
Ligand
What is equilibrium dissociation constant, Kd?
Free protein(P)*free ligand(L) divide by protein ligand complex(PL)
What is the equation for fraction of protein binding sites occupied, deter
deter = [PL]/([P]+[PL]
What is the mid point of the dissociation graph called
Kd
What is the mid point of protein-ligand interaction graph called
P50
Can myoglobin transport O2?
No, because the affinity with O2 is too high, does not release even when pressure drops in tissues(4kPa) be cause the P50 is too small. But it binds well in lungs (13kPa)
What is the tense state of hemoglobin’s purpose
more interactions, more stable, lower affinity for O2
What is the relaxed state of hemoglobin’s purpose
Fewer interactions, more flexible, higher affinity for O2 Triggers from T to R state when O2 is binding
What happens during the conformational change from T state to R state?
Breaking salt bridges between the residues at alpha 1-beta 2 interface
What are cooperative proteins
They have multiple ligand-binding sites n=number of binding sites Ka = [PLn]/[P][L]^n Deter = [L]^n/([L]^n + Kd) log (deter/1-deter) = n log [L] - log Kd
What does the hill plot slope give
measure of the degree of interaction (ie, the degree of cooperativity) between binding sites. It is called Hill coefficent (nh). It show taht nh is realted to the average occupancy of the binding site
In the hill plot of cooperativity, What does nh>1, nh=1, n<1 (rare)
If nh>1 (eg Hb/O2), positive cooperativity, binding at one site increases binding at other sites on other subunits. If nh= 1, binding is not cooperative, the sites are independent. If nh<1, negative cooperativity, binding at one site decreases binding at another site on another subunit
What is the limit of nh
theoretical is equal to the number of binding site =n experimentally, nh places a lower limit on the number of interacting sites : nh is always < n
What is the difference between the 2 model of cooperativity?
Concerted is all or none, absence of L are thought to inactive T or active R form, dia=stabilised by L binding, successive binding of L to the inactive state makes the transition to the active state more likely. Sequential, each subunit can be either T or R form, L produces change in conformation of subunit, a change in conformation in one subunit induces a similar change in an adjacent subunit. Not mutually exclusive
What are the end products of metabolism in tissues
H+ and CO2