Characterization of iron-binding phosphopeptide released by gastrointestinal digestion of egg white

Binding and solubilization of ferric iron by food peptides, released during digestion, facilitate intestinal iron absorption. In the present study, we investigated the release of iron-binding peptides during in vitro gastrointestinal digestion of chicken (Gallus gallus) egg white. The iron-binding activity of the egg white protein increased upon gastrointestinal digestion. The iron-binding fraction of egg white digesta was purified by gel filtration chromatography followed by reverse phase HPLC. Subsequently, this fraction was identified as an internal fragment of ovalbumin (DKLPGFGDS(PO4)IEAQ, 61-73 residues, GenBank AAB59956.1) by MALDI-MS/MS followed by de novo sequencing. The synthetic peptide corresponding to the identified iron-binding peptide sequence bound and increased the 59Fe-iron uptake. Further, the synthetic peptide also stimulated the iron-induced ferritin synthesis in intestinal Caco-2 cells. While, dephosphorylation of synthetic peptide completely inhibited the iron-binding activity, methyl-esterification of its carboxyl groups partially inhibited the activity. These results suggest that food derived peptides modulate intestinal iron absorption and that the isolated iron-binding egg peptide could be a potential nutraceutical for improving iron absorption.