Enzyme mimics complexing Cu(II) ion: structure-function relationships

Five peptides containing (His-X-2)-His or (His-X-3)-His motifs have been designed and synthesized to coordinate Cu(II). Structural information was obtained by various spectroscopic techniques and was used as constraint to search for local conformational energy minima by molecular mechanics. Thermodynamic stability constants of the Cu(II) chelates was obtained by F-19-NMR. The synthesized Cu(II)-peptide chelates were tested as catalysts of some important red-ox processes occuring in biological systems, in particular oxidation of ascorbate and dismutation of superoxide ion. The catalytic efficiency of the five chelates was much lower than that of ascorbate oxidase. On the contrary, two of them showed kinetic constants for superoxide dismutation about one order of magnitude lower than that of the enzyme Cu,Zn superoxide dismutase. In both cases, the catalytic properties were dependent on the peptide sequence. The relationships between structure and activity are discussed to find the structural parameters crucial for catalytic activity that can be modulated by appropriate design and synthesis of the peptides.