Model studies on iron(III) ion affinity chromatography. II. Interaction of immobilized iron(III) ions with phosphorylated amino acids, peptides and proteins.

The chromatographic behaviour of phosphoamino acids, phosphopeptides and phosphoproteins and their non-phosphorylated counterparts was studied on Fe(III)-Chelating Sepharose and Fe(III)-Chelating Superose. The phosphorylated compounds, in contrast to their non-phosphorylated or dephosphorylated counterparts, adsorb to immobilized iron(III) ions at pH 5.5 and can be desorbed by an increase in pH. Phosphoamino acids were eluted at pH 6.5-6.7, whereas monophosphopeptides and phosphoprotamine eluted in the pH range 6.9-7.5. Molecules possessing clusters(s) of carboxylic groups are weakly retained (gamma-carboxyglutamic acid, Ala-Ser-Glu5) or bound (polyglutamic acid, beta-casein) to the immobilized iron(III) ions at pH 5.5. Dephosphorylated beta-casein was desorbed at pH 7.0, whereas for elution of native (non-dephosphorylated) beta-casein, phosphate buffer of pH 7.7 was required. The homopolymer of polyglutamic acid was desorbed in the pH range 6.0-6.3, whereas copolymers of glutamic acid and tyrosine require pH 7.0-7.3 or even phosphate buffer at pH 7.7 for elution.