[R] one-site competition data // curve fitting

[Joerg van den Hoff]

On Mon, Jul 07, 2008 at 11:15:57AM +0200, Thiemo Schreiber wrote:
> Hello everyone,
> 
> I have biological data from a competition experiment where a free ligand is titrated against the binding of a protein.
> 
> Now, I would like to fit a standard on-site binding curve to this data in order to obtain the IC50 and Kd values. 
> Unfortunately I have not been able to find a package/function which allows such a fitting and calculates the results.
> 
> 
> Does anyone know if there is a suitable package available and which function to apply?
> 
> Thanks a lot.
> 
> Cheers
> Thiemo Schreiber
> 	[[alternative HTML version deleted]]


this is probably what you are looking for:

let 

x = vector of free ligand concenctrations
y = vector of correspondng spec. protein bindings

be defined in the R workspace.

than use

res <- nls( y ~ (x * Bmax) / (x + Kd), start = list(Bmax=, Kd=))

(providing some sensible start values for the free parameters , of course)

cf. `nls' manpage for details