Agonist Equilibrium Constant

[piraterach]

On a past pharmacology exam paper there is a question:

Estimate the equilibrium constant of the agonist drug from the graph.

I know that it has something to do with half the total efficacy but i don't know what to do next.

Can anyone help?

Thanks

[newtron]

I'd have to see the graph to go into more detail, but generally, an equilibrium constant is the slope of a line that represents the relationship between the concentration of reactants and products in a closed system at equilibrium.

[Peter Pedant]

SOrry this is off the top of my pretty little head.....

from the graph......Is this a Michaelis Menten plot - that is the reaction D + R = DR
it is like the one for enzymes Lineweaver Burke but that is for E + S = ES -> P
[Remember = is reversible and -> isnt]

Ligand binding Oh God I am glad I dont have to do this nowadays

Good Luck PP

[Peter Pedant]

It is like I remember

see http://en.wikipedia.org/wiki/Michaelis-Menten_ kinetics