A STRUCTURAL APPROACH TO THE COPPER SITES OF THE BLUE ELECTRON TRANSFER PROTEINS

The copper-binding regions of plastocyanins and azurins are examined by the Chou-Fasman method. Similar structural features are found in the proposed copper-binding site for stellacyanin. These structural features are related to the copper-ligand bond lengths and to the reduction potentials of the blue copper proteins. The range of reduction potentials observed in these proteins is considered to be a function of the chelating peptide loop sizes and of the nature of the amino acid side chains in the loop region. A copper core of two histidines, a cysteine and a methionine is proposed for rusticyanin with a tighter chelate loop structure in the C-terminal region than is found in plastocyanin and azurin.