A researcher is purifying a mixture of proteins at a buffered pH of 7.4. The mixture contains albumin (pI = 4.7) and myoglobin (pI = 7.0). The researcher uses a chromatography column containing a positively charged diethylaminoethyl (DEAE) cellulose resin.
Under these conditions, which of the following is the most likely outcome?
- Albumin will bind more strongly to the column than myoglobin (correct answer)
- Myoglobin will bind more strongly to the column than albumin
- Both proteins will bind equally to the column
- Neither protein will bind to the column
Explanation: This is an example of anion-exchange chromatography, where a positively charged resin (DEAE) binds negatively charged molecules. At pH 7.4, both proteins will have a net negative charge since the pH is above their respective pIs. However, albumin (pI = 4.7) will be much more negatively charged than myoglobin (pI = 7.0) at this pH. The further a protein's pI is from the buffer pH, the greater its net charge. Therefore, albumin will bind much more strongly to the positively charged column.