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Dear All, I have a 100KD protein which elutes as a mixture of 90% monomer and 10% dimer on HPLC, if I pool the monomer fractions and reload them onto the column, the elution profile is still 90% monomer plus 10% dimer, and the same is true if I do so to the dimer peak. Collectively, there seems to be a equilibrium between the monomer and the dimer. So far, I have not got crystals yet, since the purity of the protein is fairly high (99% pure), I am wondering if the lack of crystallization is caused by the heterogeneity introduced by the spontaneous oligomerization, and if so, what can I do to improve the homogeneity? Will a additive/detergent screen help (this is not a membrane protein)? Any comments will be greatly appreciated! Best, Joy