Am 14.02.2008, 20:21 Uhr, schrieb Nico <brighttomorrow from gmail.com>:
> Under 20mM KPB/500mM NaCl, it was good. But when change to 20 mM KPB/100
> mM NaCl,
> the protein precipitate out. What should I do? Change to Tris-HCl Buffer
Looks like your protein is an albumin, with elongated shape and asymetric
charge distribution. At low ionic strength they form head-to-tail
aggregates, which precipitate. You can either keep the ionic strength high
or change the pH and hence the charges on the protein.