Presumably the degree of cross linking is too high and the molecule is now huge. If you are trying to immobilise a protein for absorption processes you could try linking to an inert bead like sepharose. It would help if we knew what you are trying to do and why

Hi there,

As Paul mentioned the crosslinking degree is too high so I would suggest either to shorten the reaction or to reduce crosslinking agent concentration (or both).

We always do titration the GA concentration with a certain time on ice, say 10 min on ice with different concentration of GA. Do not forget to quench it with Tris in the end. By this way, we find the right crosslinking conditions. It is different from case to case.

I like to start by diluting glutaraldehyde to 20mM, and then add it slowly dropwise while mixing the protein(s) on ice. You can include sodium borohydride (about 10 mg/mL is good) to stabilize the crosslinks against reversal and rearrangement. And after about 10 minutes of reaction time, you can add glycine or Tris to quench the reaction (10mM is good).

Be sure to include control lanes on your PAGE: unreacted/monomer protein and MW markers.