Fe 3+ binding to ovotransferrin in the presence of α-amino acids

The ability of l -α-amino acids as synergistic anions for iron binding to ovotransferrin was investigated through electronic spectroscopy. Glycine and glutamic acid were found to form by far the most stable ternary Fe 3+ ovotransferrin-amino acid complexes. Less stable adducts were formed by amino acids with a hydroxy, amide or sulphur-containing group in the side chain, while the complexes with leucine, isoleucine, valine, lysine, arginine, tyrosine and tryptophan failed to form. Evidence is obtained that the synergistic effectiveness of the H 2 N-CH-COO − moiety is determined not only by the isoelectric point of the amino acid and the steric hindrance of its side chain, but a significant role is also played by interactions of the side chain itself with residues in the metal binding domains. Zn 2+, Cd 2+ and Co 2+ are found to bind to ovotransferrin in the presence of glycine. 113 Cd-NMR spectra on the Cd-derivative indicate that, according to the interlocking-sites model, the amino group of glycine directly binds to the metal ion.