Anita, Proteolysis and oxydation are the most common alteration affecting proteins during the course of crystallization. If you have drops of the trays that yielded crystals I would run a gel on those drops and look at the aspect of protein still around in the drop. That would give you some clues. If there was no reducing agent in the drops I would run a gel with two samples (with and without a reducing agent such as DTT or beta-mercaptoethanol for example). you could also, if you had crystals to spare (although from what you say it does not seem the case), run a gel on a crystal (it takes a little bit of practice) to characterize what is in your crystal or if you have a mass spec at hand look at the content of a crystal. How long did those crystals take to grow? Is there a skin covering your drops?
Hope this helps -- Pascal F. Egea, PhD Assistant Professor UCLA, David Geffen School of Medicine Department of Biological Chemistry 314 Biomedical Sciences Research Building office (310)-983-3515 lab (310)-983-3516 email pe...@mednet.ucla.edu
