Isoelectric Point

[rikajaj]

Can someone tell me how to find the theoretical isoelectric point of a given protein? Is there an equation? Or a search tool? I tried pubmed but I couldn't find it for the protein I need to do a paper on.

Thanks

[mith]

http://www.expasy.ch/tools/pi_tool.html

this is a predictor....

[MrMistery]

I am no expert, but an isoelectric point determination program should work with PDB files, as you need to know its 3D shape. It doesn't matter so much what aminoacids are in the protein, but rather what aminoacids are on the surface...

[woolleyy]

As I understood it a Pi detector was pretty shabby, as nothing can really substitute for hard evidence from a little experimenting...

[MrMistery]

I would think a program that would work with PDB files should get them pretty close, as it could take into account all the aminoacids on the surface. Sure, nothing beats a good isoelectric focusing, but it is good for a start.
However, i don't know if such a program exists...

[biotechatrocketmail]

There is Henderson–Hasselbalch equation which you can use to calculate raw IP of protein (see http://en.wikipedia.org/wiki/Henderson% ... h_equation). The other problem is estimation of pK values. More info about this you can find on http://isoelectric.ovh.org/ There you will be able to calculate IP for given sequence using different pKs or download all PDB database with calculated isoelectric points.