Question

I am trying to determine which protein (in a given list) will stick most tightly to a cation exchange column at pH 7. I am unsure how to go about solving this.. We are given molecular weight, isoelectic point, and number of subunits for each protein. Where should I begin?

Answer 1

The isoelectric point, pI, is equal to the pH where most of the proteins will exist as a zwitterion ion (a net charge of 0). For column chromatography, heavier proteins will elute slower than smaller ones, and proteins that have the most positive charge associated with them will also elute more slowly. lighter proteins, with pI values close to the pH where you are performing the separation at, will not really separate that well. With an example problem, this is the best that I can do.