Two site Scatchard Plots

[Michael D. Baron]

Organization: IAH Pirbright
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>In article <gayler-0509951254300001 at 198.178.220.249>, gayler at immunex.com 
>(Richard Gayle) says:
>>
>>I routinely use the curve fitting routines from Deltagraph Pro. 
>Recently,
>>I have needed to plot Scatchard graphs for receptors and their ligands
>>that require 2 site fits. What are the model and parameters to use to 
>get
>>a proper fit? TIA,
>>R.B. Gayle
>
>The model in the Ligand program developed originally by Munson and 
>Rodbard was (if I remember correctly):
>
>B=K1*F + K2*F + N*F
>
Which shows what a c**p memory I'v got.
Sorry, the correct equation should be, surely,

B=K1*R1*F/(1+K1*F) + K2*R2*F/(1+K2*F) + N*F


Where R1 and R2 are the 'concentrations' of receptor types 1 and 2,     
K1 and K2 are the equilibrium binding constants for the 2 receptor 
sites, N is a constant for non-specific absorption, and Bound and Free 
ligand are self-explanatory. Note that the model assumes that 
non-specific binding is a function of Free ligand, and this is not the 
same as the binding of labelled ligand at high concentrations of 
unlabelled ligand.


Apologies again,

Michael D. Baron