Two site Scatchard Plots

Michael D. Baron michael.baron at
Mon Sep 11 11:46:51 EST 1995

Organization: IAH Pirbright
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>In article <gayler-0509951254300001 at>, gayler at 
>(Richard Gayle) says:
>>I routinely use the curve fitting routines from Deltagraph Pro. 
>>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 
>>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

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