Fitting steady state concentration vs response values

I'm trying to fit concentrations vs. observed responses to a Langmuir 1:1 model but have not discovered any straight forward method. Does anyone have a suggestion on how to fit this data to obtain Rmax and KD?

Hi,

Use the steady state model.
The requirement for this model is that the response measure point is at steady state.
Kind regards

Arnoud

Thanks Arnoud for the response. I left out a few details that may have better framed the question.

I captured a his-tagged receptor and injected over its binding partner for 120 seconds. The his/anti-his interaction decayed about 35% during the association so I took the max response just a few seconds after injection (very fast on-rate). I then plotted those responses on the attached chart as they are more representative of the response at that concentration. I’m wondering if there is a way to fit this curve to obtain the rmax and KD as I can’t change the response point the Biacore software uses for determining response and would prefer not to repeat experiment with shorter associate time. Many thanks in advance !

Hi,
The formula for fitting the steady state is: Y = Conc*Rmax/(KD+Conc).
It can be done in Excel. Search for 'excel fitting with solver' on the web and you get some tutorials.
Also most commercial graph-software can do this fitting, so you are not dependent on your SPR software.
The model is often one site binding or hyperbola.

Kind regards
Arnoud

Thank you Arnoud. What I’m struggling with is that I am trying to calculate both KD and Rmax from this response vs concentration plot. I couldn’t find a straightforward solver tutorial either for fitting this curve. Thanks for your help.