What does a common cation exchanger like carboxymethyl (CM) bind to?

The common cation exchanger, such as carboxymethyl (CM), is designed to interact with positively charged molecules. This is due to the nature of its functional groups, which are negatively charged at physiological pH, allowing them to attract and bind cations. Therefore, a cation exchanger is particularly effective at binding positively charged amino acids or peptides.

Carboxymethyl groups have carboxyl functional groups that ionize to become negatively charged, enabling these exchangers to facilitate the binding of cations through electrostatic interactions. This principle underlies many of the methods used in biochemical purification and separation techniques, where the desired compounds can be selectively retained or eluted based on their charge characteristics.

Importantly, while cation exchangers are selective for positively charged entities, they do not bind negatively charged peptides or neutral proteins effectively, making them unsuitable for those categories. Additionally, they do not bind both positively and negatively charged compounds simultaneously, as this would contradict the basic mechanism of charge-based separation employed in these types of exchangers.