I need to calculate the KD for enzyme-ligand using the quadratic equation as shown in the pic. Graph pad prism or origin software do not have these equation by default. However when I am trying to enter my own equation, both the software are not giving correct results. Perhaps I am making a mistake in the format of entering the equation. I shall be grateful if someone could guide me or send me the prism file settings for same equation or tell me the software that has this equation setting by default.
If you can give me some details about your data (what your x- and y-values are), I might be able to provide some help concerning Origin splving the equation.
Feel free to send a PM.
Best regards,
Moritz
Hello,
I have an Origin equation formatted for this.
Using Origin:
1) Create a new fitting function
2) Choose expression
3) Independent variable will be x, dependent will be y, parameter will be K (for Kd), constant will be A
4) In "function body" enter: 1/(1+(K/(x-0.5*(A+x+K-((A+x+K)^2-4*A*x)^0.5))))
5) On the top, switch over to constant, enter your constant value (for whichever concentration was kept constant)- you can change this each time if you have different constant values.
6) Hit "next" until you get to "finish"
You can now calculate your Kd with this equation. This will only work if you have a constant concentration, A, of either enzyme or ligand and then a changing concentration of the other for your x values. The K value that Origin calculates will be your Kd.
Let me know if this doesn't work!
Hi Taran can you send me the .fdf function file ?
Thanks !
Massimiliano
A more general variation that for me work:
I add a third variant call C, or maximum
Y=C/(1+(K/(x-0.5*(A+x+K-((A+x+K)^2-4*A*x)^0.5))))
Hi Juan, Can you please send me .dfd function file.
I have tried but I got error all the time. Error showing "fit did not converge and parameter K values always showing 1.
Thanks
Shadabi
Juan Pablo Fuenzalida Werner ;
Hi,
Can you please send me .dfd function file.
I have tried but I got error all the time. Error showing "fit did not converge and parameter K values always showing 1. My origin software is OriginPro8.5
https://www.nature.com/articles/s41598-017-17072-z
Beyond the Michaelis-Menten equation: Accurate and efficient estimation of enzyme kinetic parameters
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