On the role of strain in blue copper proteins

Theoretical investigations of the structure and function of the blue copper proteins are described. We have studied the optimum vacuum geometry of oxi dised and reduced copper sites, the relative stability of trigonal and tetr agonal Cu(II) structures, the relation between the structure and electronic spectra, the reorganisation energy, and reduction potentials. Our calculat ions give no support to the suggestion that strain plays a significant role in the function of these proteins; on the contrary, our results show that the structures encountered in the proteins are close to their optimal vacuu m geometries (within 7 kJ/mol). We stress the importance of defining what i s meant by strain and of quantifying strain energies or forces in order to make strain hypotheses testable.