Question

what is an isoelectric point of a protein? explain how one can use this property to separate proteins. Why is the selection of a buffer with proper ph important

Answer 1

In proteins the isoelectric point (pI) is defined as the pH at which a protein has no net charge. When the pH > pI, a protein has a net negative charge and when the pH < pI, a protein has a net positive charge. The pI varies from protein to protein. This is the reason ion exchange is useful for separating proteins.

If a buffer containing more than one protein is used with an anion exchange resin, then the most negatively-charged protein will be most attracted to the stationary phase and will therefore elute last and the protein with the highest positive charge will elute first.