correlation of IC50 to receptors/enzyme molecules

P.C. PC at no.email.sorry
Fri Feb 6 15:39:05 EST 2004

it has been more than 10 years I passed an exam on enzyme kinetics, and 
that was not my favorite topic... But common sense dictates that the 
situation will very much depend on the mechanism of inhibition, relative 
concentrations of the enzyme, substrate and inhibitor, and the 
stoichiometry of binding. If it is a simple competetive inhibition, and 
the stoichiometries of the E-S and E-I complexes are same, and you have 
a classic case of E<<S, then, I think IC50 will solely depend on 
relative concentrations of S and I.

On the other hand if E is not << I and you have a sort of inhibitor that 
irreversibly binds your E and inactivates it (forming a dead-end 
complex), for example, then its IC50 will of course directly depend on 
concentration of the enzyme (E).

what kind of inhibitor is it?

otherwise, look into some good enzymology book, like Fersht's Enzyme 
structure and mechanism (I remember everybody loved it).



interpreneur_org at yahoo.com wrote:
> In a binding or kinetic assay, how does the IC50 of a compound change with respect to the number of receptors/enzyme molecules available? Is it linear (e.g: 10 times more protein leads to a 10 fold increase in the IC50)? Or not? And what is the mathematical equation explaining this?
> Thanks!
> Lisa.
> http://biowww.net/mynews/tree.php?group_name=bionet_molbio_proteins&begin=0

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