ERLIC of Phosphopeptides

ERLIC of peptides is normally performed with a PolyWAX LP™ column at a pH ~ 2.0, low enough to uncharge carboxyl- groups in peptides. Under these conditions, phosphate groups retain their negative charge and are electrostatically attracted to the column. This attraction is not sufficient to overcome the electrostatic repulsion from the two basic groups in a typical tryptic peptide (the N-terminus and the Lys- or Arg- residue at the C-terminus), which is why anion-exchange has not been used for selective isolation of phosphopeptides from tryptic digests. Phosphate groups are quite hydrophilic, though. In the ERLIC mode the combination of electrostatic attraction and hydrophilic interaction does suffice to pull phosphopeptides away from the nonphosphorylated peptides in a tryptic digest. This is clear from the following example, which contrasts retention of tryptic peptides from beta-casein on the same column in the ERLIC mode and in the anion-exchange mode.

Column Name : PolyWAX LP™ Columns

Compound Name : Phosphopeptides