A pmr study of the effects of pH and anion and metal ion binding of the histidyl residues of ovotransferrin.

High resolution proton magnetic resonance studies of ovotransferrin show clear resolution of four groups of C(2)-H histidyl resonances to low field of the major aromatic envelope. Titrations of the protein in the absence and presence of synergistic anions, oxalic acid, malonic acid, and 2,6-dipicolinic acid, and anions plus metal ions reveal that six histidines are involved in the binding sites. These histidines, three in each binding site, are near to one another. In each binding site one histidine is involved in binding to anions and two are involved in binding to metal ions.