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drestef
Germany
1 Posts |
 Posted - 03/20/2011 : 3:51:17 PM
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Origin Ver. and Service Release (Select Help-->About Origin): 8.0
Operating System:Windows 7
Dear Origin community,
I am having some problems concerning determination of an enzyme Kd. I am using a competitive titration method:
Competitor 1 forms a 2:1 complex with the ligand and can be photometrically detected. The reaction Kd is given by literature.
Competitor 2 forms a 1:1 complex with the ligand of which Kd is to be detected.
For the experiment, competitor 2 is added to a mixture of ligand and an excess of competitor 1. competitor 2 picks up substrate from competitor 1, so the concentration of the ligand-competitor 1 complex is reduced and the light absorbtion decreases. I found an equation that seems to perfectly fit to the experiment and I have already examined it using a maths calculation software - The graph is shown below and also seems to perfectly match the data. The equation is:
a/b = (x/(c - y) - 1)/((d/y - 2)^2 y)
where
a = Kd of competitor 2 (which is the parameter of interest),
b = Kd of competitor 1,
c = starting concentration of the substrate-competitor 1 complex
d = total concentration of competitor 1
The variables are
x = concentration of competitor 2 and
y = concentration of substrate-competitor 1 complex
The problem is that I am not able to get the function compiled in origin. The actual fit has not even taken place yet. It would be great if soumeone could give me a hint or perhaps even send me an origin project file containing the equation. I need this for my master's thesis and I can't find anybody who is able to help me with this.
Best regards from germany,
Steffen
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Penn
China
644 Posts |
Posted - 03/21/2011 : 04:24:48 AM
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Hi Steffen,
I am not sure whether your equation has analytic solution. Origin currently does not support the fitting of implicit function, that is to say, the fitting function must can be written as y=f(x). If you have make sure that your fitting function can be written as y=f(x), please follow this tutorial.
Penn |
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cc261
22 Posts |
Posted - 03/27/2011 : 10:22:13 AM
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| try a soft named Auto2Fit or 1stOpt, they support nonlinear regression for implicit function perfectly. |
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Enzyme Kd determination - equation won't compile