At which pH would proteins A and B adhere to a cation-exchange column?

Proteins exhibit different charge properties at various pH levels due to the presence of ionizable side chains, which can either accept or donate protons. In a cation-exchange column, positively charged proteins are attracted to negatively charged groups on the column matrix.

At a neutral pH of around 7.0, many proteins maintain their native charge states that can vary from neutral to slightly basic depending on their amino acid composition. If proteins A and B have pI (isoelectric point) values below this pH, they will carry a net negative charge and will therefore not adhere to a cation-exchange column at this pH, as they are not positively charged.

At pH values lower than 7.0, such as 3.0, the environment is acidic, and proteins with pI below this pH would be positively charged and likely adhere to the column. Conversely, at alkaline pH values like 9.5 or 11, many proteins would carry a net negative charge, especially those with pI values higher than the pH, leading to repulsion from the negatively charged column.

Overall, a pH of 7.0 represents a balance point where the charge characteristics of proteins A