BINDING OF COPPER AND ZINC IONS TO POLYPEPTIDES CONTAINING GLUTAMIC-ACID AND TYROSINE RESIDUES

The binding of Cu++ and Zn++ ions to three polypeptides containing Glu and Tyr residues, (Glu Tyr Glu)n, (Glu-Glu-Tyr-Glu)n and (Glu-Tyr-Tyr-Glu)n has been investigated by absorption spectroscopy, fluorescence and circular dichroism. Difference absorption spectra show that Zn+- slightly perturbs the absorption spectrum of the tyrosyl residue whereas Cu++ binding is accompanied by the appearance of a strong absorption band around 245 nm. The fluorescence of the tyrosyl residue is enhanced by Zn++ ions while it is quenched by Cu++ ions. Cation binding induces a conformational change of the polypeptides from a random coil to an α-helix, Mg++ ions do not elicit any of these phenomena. © 1979.