EXAFS Investigation on the Iron(III) Binding Sites of Hen Phosvitin

EXAFS spectroscopy has been applied to investigate the nature and the stereochemistry of the iron(III) binding sites in the protein phosvitin from chicken eggs in water solution with an iron/protein molar ratio of 10/1 at pH 7.2. The main result is that the iron atoms are bound to the protein in an octahedral environment and that the main binding sites are provided by the oxygen atoms of serine-bound phosphate groups at 1.93 (2) Å from the metal. The average number of bound phosphate groups is 4.4 (9) per iron atom, hexacoordination being achieved upon binding of other possible donors from the protein or solvent water molecules. No evidence has been found of short Fe–Fe interactions, so that, on the basis of our data, it can be stated that iron is not essentially involved in a polynuclear structure with Fe–O–Fe bridges.