x*******i
发帖数: 32 | 1 Hello There,
We have a protein (pI = 8.9, 10 mg/mL, MW 100 K) precipitated in 10 mM
phosphate buffer (pH around 7) after overnight storage at 4 degree. The
precipitate will be soluble again when warming up solution to room
temperature. Addition of NaCl will prevent precipitation. Other common
buffers are OK not causing precipitate.
Hypothesis is ionic cross-linking. Phosphate ion has intense negative charge
density and working as the cross-linking agent, its multiple negative
charges interact with positive proteins to cause precipitation.
The ionic interaction between negatively charged phosphate and positively
charged protein is supposed to be weak and transient. Perhaps only a small
percentage of phosphate ions in buffer are enough to initiate precipitation.
Is there any direct way to prove the above hypothesis?
Thank you very much! | l**j
发帖数: 651 | 2 what are the other common buffers have been tested?
charge
【在 x*******i 的大作中提到】
: Hello There,
: We have a protein (pI = 8.9, 10 mg/mL, MW 100 K) precipitated in 10 mM
: phosphate buffer (pH around 7) after overnight storage at 4 degree. The
: precipitate will be soluble again when warming up solution to room
: temperature. Addition of NaCl will prevent precipitation. Other common
: buffers are OK not causing precipitate.
: Hypothesis is ionic cross-linking. Phosphate ion has intense negative charge
: density and working as the cross-linking agent, its multiple negative
: charges interact with positive proteins to cause precipitation.
: The ionic interaction between negatively charged phosphate and positively
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