When I run the fitting in BiaEvaluation I always get sharp lines, I mean the lines don't go smoothly with the curve, always go with right angles around the curve without any curvature (Fig 1), do you know why and how can I resolve this
First make sure that the concentration values you put in are right.
Then choose the proper parts for association and dissociation.
Select a 1:1 model.
What you can try is to do the fitting in little steps.
1) fit the dissociation only.
2) fit the association and dissociation but use the value of 1 and set it constant. In addition, set the RI and drift to constant zero.
3) repeat 2) but change the initial value for ka a factor 10 up or down
4) when the fitting looks better, repeat with the reported values from 3) and let float the RI and drift if necessary or add a mass transport component.
All the contributions of RI, drift and mass transport should be small.
When you said "use the value of 1 and set it constant." you mean use the 1:1 model?
The problem is that when I am trying the Biaevaluation handbook procedure for fitting of the model file came with Biacore, I still get the same right angle fit although I am following the same procedure mentioned in the handbook?
The reason why fittings sometimes go wrong is that the initial values are too far from the actual values and the fitting procedure gets stuck in the wrong values.
Please look at www.sprpages.nl/data-fitting/models for more explanation.