Structural Studies of Biological Polynuclear Iron(III)
Several reports97,103–5 have appeared concerning the interaction of iron with phosvitin, a phosphoglycoprotein of molecular weight 35 000 containing 6.5 per cent carbohydrate, which accounts for 60 per cent of the protein-bound phosphate in egg yolk106–8. In the presence of oxygen and phosvitin, iron(II) chloride is rapidly oxidised to a bound form of iron(III), with accompanying release of phosphoryl groups from the protein103–5. This iron(III) phosvitin, containing about 9 per cent iron by weight has not been characterised with respect to the structure of the bound iron. Nutritional reports109 indicating that dietary eggs inhibit iron absorption stimulated further investigations of the interaction between iron(III) and this protein97. To mimic the nutritional forms of phosvitin commonly available in the diet, iron(III) (as the nitrilotriacetic acid chelate) was presented to phosvitin both before and after treatment of the protein with boiling water. These procedures led to the isolation of two metalloproteins, green and brown iron(III) phosvitin, respectively, which bind about 7 per cent iron by weight to a final phosphorus: iron ratio of 2. Both derivatives have been shown to contain polynuclear iron(III) but in sites of different co-ordination geometries.
KeywordsCent Iron Mossbauer Spectrum Cent Carbohydrate Green Iron Octahedral Iron
Unable to display preview. Download preview PDF.