Oscar Castellani

Egg yolk phosvitin: preparation of metal-free purified protein by fast protein liquid chromatography using aqueous solvents

Two chromatographic methods for hen egg yolk phosvitin purification avoiding organic solvents were evaluated. Hydrophobic interaction and ion-exchange chromatographies were applied to isolated phosvitin. Hydrophobic interaction chromatography has better capacity than ion-exchange chromatography to fractionate phosvitin in their different polypeptides, but its protein yield was lower (0.7 vs. 1.7% of egg yolk dry matter). Finally, ion-exchange chromatography was selected and allowed to fractionate phosvitin polypeptides, including the recovering of phosphoproteins with high electrophoretic mobility: phosvettes. Highly purified (>98%) and free metal protein was obtained in reduced time. Phosvitin polypeptide heterogeneity was evidenced.

Egg Compounds with Antioxidant and Mineral Binding Properties

Ovotransferrin is a monomeric egg white glycoprotein, belonging to the transferrin family of proteins widely distributed in various biological fluids. It has the same structural characteristics as hen serum transferrin, because these proteins derive from the same gene and differ only by their attached carbohydrate (Mizutani et al. 2001 ). This protein has a molecular weight of 77 kDa and is made up of two domains, an N-domain and a C-domain, with a short linking region (Williams 1982). Each domain has a binding site for metal ion, tyrosyl, histidyl, arginyl residues being implicated as effective in this action; the site requires synergistic anion binding (Oe et al. 1989). Ovotransferrin binds iron very strongly, in particular Fe3+, since its dissociation constant (KDiss) is 10−24 M (Stevens 1991); it can bind two iron atoms per molecule. The order of iron binding is pH dependent; at pH 6.0 it binds first to the C-domain, but at pH 8.5 it first binds to the N-domain. The function of ovotransferrin is generally accepted as iron transport. It can bind other metal ions, including toxic ones. Mizutani et al. (2005) report that the aluminum-bound form is almost