The peptide-based pharmaceutical composition of claim 2 wherein said medically useful metal ion-binding domain is selected from the group consisting of Cys!n, Cys-(R2)-Cys!n, Cys-(R2)-Pen!n, His-(R2)-Cys!n, His-(R2)-Pen!n, His!n and His-(R2)-His!n wherein, n is a number between 1 and about 6; and R2 is an amino acid sequence containing from 1 to about 20 amino acids. 5.