Metal chelates of glycine and glycine peptides.

Since the advancement by Smith et al. (l-4) of the theory that metal ions are chelated simultaneously to enzyme protein and substrate in various polypeptidases, the nature of metal binding to peptides and proteins has become an important as well as an interesting problem. The chelate structures proposed by Smith (3), and later somewhat revised (5, 6), indicate that the metal is bound, at least to the substrate and possibly to the enzyme protein, through the polar groups in two or more adjacent peptide linkages. The affinity of binding, but not the specific groups involved, can be determined for the interaction of metal ions with proteins. It would, therefore, be of interest to study the affinity of the binding to simple peptides for which the nature of the groups bound to the metal ion can be specified with considerable certainty. The accumulation of sufficient data of this type may make it possible to deduce the types of linkages involved in metal-protein combinations. As an approach to this general problem, the present paper describes an investigation of the interactions of glycine peptides and glycine with Mg(II), Mn(II), and Cu(I1) ions.