Question

use pK_a = 3.2 the a-COOH group, pK_BH = 8.0 for the a-NH₂ group, and the following values for dissociation constants for side-chain groups.

Amino Acid Dissociation Constant of Side Chain Group

Aspartic Acid 3.9 (pK_a of COOH)

Glutamic Acid 4.2 (pK_a of COOH)

Histidine 6.0 (pK_BH of =N)

Lysine 10.5 (pK_BH of NH₂)

Using the information above.

For a mixture of the peptides listed below, predict the order in which these peptides would elute from a cation-exchange column using gradient elution from pH 2 (start) to pH 11 (end).

His-Gly-Ala-Glu Lys-Gly-Ala-Glu Asp-Gly-Ala-Glu Lys-Gly-Ala-Val