On Wed, 2011-11-16 at 09:26 +0000, Tom Murray-Rust wrote:
> That way you should be able to
> quickly identify any hits that are due to salt, and which are likely
> to be your protein.
Just a footnote to Tom's excellent comment:
It is possible to have actual protein crystals to grow alongside salt
crystals. It is also possible for salt crystals to grow only when
protein is present and not with protein storage buffer. I've seen both
things happening. My point is that seeing salt crystals in the "buffer
drop" is suggestive, but not an absolute proof. It stinks to fish out a
(usually heavy and unyielding) salt crystals just to see three
super-bright spots, but that is the only 100% conclusive way I know
(channel-penetrating dyes and UV microscopy have their limits).
On a more informative note, I used protein in PBS once (not because it
was unstable, but rather because I was lazy), and it surprised me how
few salt crystals I got with standard screens. I tend to think
phosphate will be trouble with divalent cations (calcium and magnesium
primarily), but I presume the solubility is somewhat pH dependent and
that alleviates the problem to some extent.
And of course, in the described scenario of protein that needs phosphate
for solubility there isn't much choice. (But perhaps buffer screening is
in order).
Cheers,
Ed.
--
Hurry up, before we all come back to our senses!
Julian, King of Lemurs
