Question

In what order would histidine, serine, aspartate, and valine be eluted with a buffer of pH 4 from a columncontaining an anion-exchange resin (Dowex 1)?

Short answer

The order of elution of amino acids are shown below

Histidine> Valine> Serine> Aspartate

Step-by-step solution

Anion exchange resin

These are positively charged groups binds to anions by exchanging there negatively charged ions. Thus, they retain anions in the column.

Order of elution

Anion exchange resin releases amino acids opposite to what happens in cation exchange resin. Cation exchange resin releases aminoacids with low isoelectric point value whereas anion exchange resin releases aminoacids with high pI value. Histidine pI value is greater than the given phgives aminoacid a positive charge. Thus, same charge carrying aminoacid and resin repell each other and elute first in the coloumn. The order of elution depends on the isoelectric point value of the given aminoacids as follows

Histidine (7.64), Serine (5.70), Aspartate (2.98), Valine (6.02)

Thus, the order of elution can be written as Histidine>Serine>Aspartate>Valine