Dear Jinjin:
Malic acid, a diprotic acid, has a pKa of about 3.4 for the first dissociation
and a second at about 5.1. So it is best as a buffer within a pH range of about
2.4 to 6.1, and it at its best around best in the range of 3.4 to 5.1. If the
pH of your solution is indeed 7, then it is doing little to buffer it (but the
small amount of tris might).
Many diprotic and polyprotic organic acids chelate metal ions.
If you could substitute a different dianionic salt in the mother liquor, like a
sulphate, it might help.
Bill
On Wed, 9 Jan 2008 18:42:06 -0500
JINJIN ZHANG <[EMAIL PROTECTED]> wrote:
Dear All,
I have got large and nice crystals in a condition that contains 40%
glycerol, 75 mM DL-Malic Acid pH7.0, and that's it! No precipitant?! No
buffer?! I'm so comfused. As far as from the product website, the Malic Acid
has no buffering function. I don't know whether it's a precipitant. The protein
itself was stored in a buffer contains 20mM Tris pH7.5, 150mM NaCl and 10%
glycerol. I'm having difficulties in getting heavy metal bound derivatives. I
was wondering whether the Malic Acid interferes heavy metal binding? Does
anyone has any success with crystals grow with similar conditions? Any comment
and suggestion is highly appreciated.
Regards,
Jinjin Zhang
