The fraction ($f$) of protein with ligand-bound is
$ f=\frac{P_T+L_T+K_D-\sqrt{(P_T+L_T+K_D)^2-4P_TL_T}}{2P_T} $
It is a function of
- total protein concentration ($[P_T]$)
- total ligand concentration ($[L_T]$)
- binding affinity ($K_D$)
not just the molar ratio between the protein and ligand ($[P_T]:[L_T]$). This Web app will help you better understand the relationship between these 4 variables.
The quadratic binding ratio formula included in this web app has also been discussed in detail in this paper that I recommend as a must-read paper for anyone who plans to measure binding affinity:
Jarmoskaite, I., AlSadhan, I., Vaidyanathan, P. P., & Herschlag, D. (2020). How to measure and evaluate binding affinities. eLife, 9. https://doi.org/10.7554/eLife.57264
Open Source/Development
The source code and all revisions are available on GitHub
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