protein precipitation - (Feb/12/2009 )

Do proteins precipitate at their pI, if so do they become non-functional when they precipitate?
does that mean that to be a functional protein the always need to carry charge?

You, actually, have right answer on all your questions Yes, protein mostly precipitate at they pI (but there are some exceptions) and they lost almost all activity at pI. And you are right again, asymmetric charge distribution is the basic for all protein-protein (and other biomolecular) interactions and enzymatic activities.

Oleksii