CD and Exafs Study of the Interaction Between Phosvitin and Copper(ii) Ions

The interaction of copper(II) with phosvitin has been investigated in the pH range 6.5–10.5, through CD, EPR, and EXAFS spectroscopies. Three types of tetragonal chromophores differing for the number of nitrogen atoms, have been identified at different pH values. EXAFS investigations of a sample containing 10 mol of copper per mol of protein, at pH 8.6, support the main conclusions of CD and EPR spectroscopies indicating the presence of tetragonally bound copper ions with four equivalent very short Cu-donor distances of 1.93 A and the involvement of histidine groups in binding. Histidines seem to constitute the principle side-chain residues involved in copper binding. Phosvitin appears to be able to provide different donor groups and stereochemistries, depending on pH and the nature of the metal ion.