Re: Prestaining Proteins for Isoelectric Focusing

First off, I think it is very hard to assess whether a stain will change 
the pI or modify the proteins physical qualities. In fact, I would need a 
lot of convincing to accept that anything that binds strongly to a protein 
would NOT affect it's mobility in a gel of whatever kind. Indeed it is not 
uncommon that a single unwanted acetylation of a protein can shift it's 
migration in a gel. Having said this, it should be possible to make do, as 
long as you systematically compare runs under equal conditions. Many 
methods involve casting a gel with the dye in it, colouring the protein as 
it migrates through it. I have done this using Coomassie Brilliant Blue 
(CBB), but that was in a denaturing gel. IEF, by nature, implies a 
gradient in pH, so you would need a dye which would show up at all pH-es 
(excluding CCB, BTW). I would go for a shielded fluorophore, but would 
forget on hoping to leave the pI unaffected. Rather: as little affected as 
possible.

The www is a wondrous place. I made a search using key-words like: method, 
non-denaturing, protein and prestaining and fished out several "leads" as 
to what staining could be used. Same thing for coloured protein standards. 
There is Biorad, but there is also Novex, Invitrogen...

I hope this helps a bit. Good luck with your project!

Erik