Deamidation converts asparagine (and, more slowly, glutamine) into aspartic acid or isoaspartic acid, through a cyclic succinimide intermediate. It is fastest where asparagine is followed by glycine, and it speeds up with moisture, higher pH and higher temperature.
The product is 0.98 Da heavier and carries an extra negative charge, so it often shows as a nearby HPLC peak and as a +1 Da shift by mass spectrometry. Dry, cold storage slows it down.
See also
For in vitro laboratory research only. Not for human or veterinary use. This library describes chemistry, analytical methods and published laboratory research; it gives no guidance on use in people or animals.