You might be giving too much importance to the THEORETICAL pI of the protein. If it's supposed to be well charged at pH 7,4 (only a titration curve, and not simply knowing the pI will tell you this) and it's still precipitating, the problem might be due to a bad fold, for instance, or to the lack of salt ...
I've heard people saying that proteins with high pIs are more difficult to work with, but to be honest I don't know where that fear comes from. Carlos Em 02/03/2012, às 05:55, Artem Evdokimov escreveu: > This pH is generally incompatible with Ni IMAC, sorry :) If you have a > high pI your best bet is to employ ion exchange as primary capture, > specifically SP resin or if you're really lucky - CM resin. There are > only relatively few proteins in E. coli that bind to CM resin at pH 5 > and virtually none (one-three) that will bind at pH 8. If your protein > still binds, then you're good to go. > > Artem > > On Thu, Mar 1, 2012 at 10:49 PM, anita p <crystals...@gmail.com> wrote: >> Hi all, >> Has anyone used sodium acetate buffer pH (4-5) for purifying histag protein >> on Histrap column (AKTA) followed by SEC? >> My protein has a pI of 9. I tried pH7.4 but it has precipitation problems. >> While doing buffer screening using 24 well hanging drop I found that lower >> pI onces are clear, so just thinking can I use Na acetate at pH 5 for whole >> purification??? >> >> >> Thanks in advance >> Anita
