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Megha, If you want to prepare your sample at a pH below the pI, you will want to use a cation column. Enzymes at pH's below their pI have an overall positive charge. Cation exchange is a column which has a negative charge, thus it will bind to positively charged proteins. I would suggest looking at GE healthcare's chromatography section. They have pretty good books (or chapters rather) that describe all kinds of chromatography and will guide you in the right direction. http://www4.gelifesciences.com/aptrix/upp01077.nsf/Content/protein_purification~ion_exchange# The have detailed information about pH stability of each resin type as well. Kelly ******************************************************* Kelly Daughtry PhD Candidate Department of Physiology and Biophysics Boston University School of Medicine 590 Commonwealth Ave R 390 Boston MA, 02215 (P) 617-358-5548 ******************************************************* On Fri, Jan 8, 2010 at 10:01 PM, megha goyal <[log in to unmask]> wrote: > Dear all, > > our protein is stable in acidic pH at a pI of 6. we do not have any tag in > it and it is expressed in inclusion body form. which ion exchange > chromatography will suit it cation or anion exchange and do i use a strong > or a weak ion excahnge resin. > > thanks and regards.