Nuclear quadrupole interaction of111Cd on type-1 Cu-sites in blue copper proteins

The nuclear quadrupole interaction (NQI) of¹¹¹Cd substituted for Cu(II) on type-1 sites in blue copper proteins is characterized by high values of ₀ in the region of 300 Mrad/s, close to that for the catalytic zinc site in alcohol dehydrogenase. Type-1 Cu has usually two sulfur ligands and two nitrogen ligands and in some cases an oxygen ligand in either a distorted tetrahedral geometry or in a trigonal bipyramidal geometry. The near tetrahedral arrangement together with the ligand sphere containing the same number of sulfur ligands explains the value of ₀ in the blue copper proteins. The present work determined the partial NQI for methionine using the known structure of azurin. This value was then used in the angular overlap model to calculate the NQI for ascorbate oxidase the structure of which is also known and gave good agreement with experiment. NQI data for laccase and stellacyanin the structures of which are unknown, are also given.On leave from Technische Universität München, Germany.