On Feb 18, 9:37 pm, "Dr Engelbert Buxbaum"
<engelbert_buxb... from hotmail.com> wrote:
> Am 14.02.2008, 20:21 Uhr, schrieb Nico <brighttomor... 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
> > or.....
>> 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.
I agree with Dr Buxbaum. Try increasing the NaCl concentration (you
could try between 200-500mM if you really need to drop the
concentration), clearly the main reason for the precipitation.
Changing the buffer/pH will probably not help much...