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Hi, Yes. This is very similar to what we've observed previously - and the answer in those earlier cases was - oligomerization. This is doubly likely since you have SEC that suggests this possibility as well. An additional consideration is that your ladder follows (at least by eyeballing) an almost exact log-scale pattern both in terms of gel retention and in terms of band intensity. This suggests a classical distribution of weakly attractive molecules, forming a series of homo-oligomers [N] <-> [N2] <-> [N3] ... <-> [Nn] The fact that you are not observing a huge smear suggests that the rate of exchange is pretty slow... Why does AUC disagree: hard to say for sure, might be for instance a difference in buffer, temperature, or sensitivity of your particular AUC set-up versus the SEC one. Good luck, Artem -----Original Message----- From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of Jacob Keller Sent: Wednesday, November 19, 2008 3:57 PM To: [log in to unmask] Subject: [ccp4bb] Native Gel Charge States Vs. Conformations Vs. Oligomeric States Dear Crystallographers, I am having trouble interpreting the attached native gel (which is very repeatable, under various conditions). Is it tenable that various charge states or conformations could account for this behavior, or must it be various oligomeric states? AUC results seem to show only monomers, whereas SEC shows a series of peaks. Mass-spec shows no post-translational mods. Anyone have any similar experiences, or references? Thanks, Jacob ******************************************* Jacob Pearson Keller Northwestern University Medical Scientist Training Program Dallos Laboratory F. Searle 1-240 2240 Campus Drive Evanston IL 60208 lab: 847.491.2438 cel: 773.608.9185 email: [log in to unmask] *******************************************