What is the role of anion-exchange chromatography in protein separation?

• A. Separates based on molecular weight
• B. Elutes cations from a positively charged medium
• C. Separates based on varying negative charges
• D. Filters molecules based on shape

Answer: (C)

Anion-exchange chromatography is specifically designed to separate proteins based on their net charge. In this technique, the stationary phase consists of a positively charged resin that attracts and binds negatively charged molecules, which are primarily anions, including proteins with varying negative charges.

As the sample passes through the column, proteins with stronger negative charges will bind more tightly to the positively charged medium, while those with weaker negative charges will elute more quickly. By gradually changing the conditions in the column—such as increasing the salt concentration—different proteins can be selectively eluted based on their varying negative charges, allowing for effective separation.

The other choices do not accurately reflect the principle behind anion-exchange chromatography. For instance, separating based on molecular weight refers to size-exclusion chromatography, not anion-exchange. Eluting cations from a positively charged medium is not correct, as anion-exchange specifically targets anions, not cations. Lastly, filtering based on shape relates to molecular sieving or size-exclusion chromatography rather than charge-based separation. Thus, the correct understanding of anion-exchange chromatography revolves around the separation based on varying negative charges of the proteins being analyzed.