Hello,
That first equation is to be used when you have a monomer-dimer in fast
exchange. The second equation is to be used when you have protein-ligand
in fast exchange. Neither equation will make sense in other circumstances
and so could easily give funny answers. (But I also seem to remember that
the parameter fits could be sensitive to the data for at least the second
equation, in cases when the data was not sufficiently sampled for the
whole curve.)
I've attached a PDF file describing these two equations, in case anyone is
interested. (The first equation below is described in the second section
and the second equation below in the first section, to be confusing.)
Wayne
On Mon, 24 Jan 2011, shixiong lua wrote:
> hi team,
>
> i was using the "follow shift changes" function of ccpnmr and discovered a bug.
>
> when i chose the fiiting function: A((B+4x-sqrt((B+4x)^2-(4x)^2))/4x-c), the Kd fitted
> was all negative values.
>
> i thus changes to another function A(B+4x-sqrt((B+x)^2-4x)) which does not fit very
> well but gives sensible Kd values.
>
> When i was looking at the <fit graph> window for each spin system, i manually changed
> the fitting function from the drop list in the <fit graph> window itself. But instead
> of reporting an insensible negative Kd value, it showed a reasonable value.
>
> please look into this matter
>
> --
> Warm Regards,
>
> Lua
>
>
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