If protein A has a pI of 3.1, protein B has a pI of 6.8, and protein C has a pI of 8.9, which protein would elute FIRST from a cation exchange column at pH 7?

Question

Quizplus · Accepted Answer

At a pH of 7, the cation exchange column will be negatively charged and will bind positively charged proteins. Protein A has the lowest pI, meaning it has more positively charged residues at pH 7 than the other two proteins. Therefore, protein A will bind to the column more strongly and will elute last. Protein C has the highest pI, meaning it has fewer positively charged residues at pH 7 than the other two proteins, and will therefore elute first. Protein B will elute between proteins A and C. Thus, A will elute last and C will elute first.

If Protein a Has a PI of 3