Two site Scatchard Plots
Michael D. Baron
michael.baron at bbsrc.ac.uk
Wed Sep 6 06:21:34 EST 1995
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
Where 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.
LIGAND did a least-squares fit to this equation, without transforming to
Scatchard plot co-ordinates, as these are poorly defined mathematically
(due to the same datum (Bound ligand) appearing on both axes). You should
set Deltagraph to do the same, I guess, assuming it can do non-linear
least-squares fitting.
Hope this helps
Michael D. Baron
More information about the Bio-soft
mailing list