Iron K-edge near-edge (XANES) and extended X-ray absorption fine structure (EXAFS) spectra have been measured for the purple acid phosphatase from beef spleen and for several oxo-bridged model complexes. The XANES show a shift of the absorption edge to lower energy by 2.0 eV upon reduction of the purple form of the enzyme to the pink form, consistent with reduction of one of the iron atoms. Fourier transforms of the EXAFS data of the purple form of the enzyme show three peaks, assigned to Fe-O(N) (first shell), Fe-Fe and Fe-P or Fe-C (second shell), and Fe-C(N) (imidazole, third shell) scatterers, in order of increasing distance. Best fits of the individually back-transformed peaks using theoretical functions are consistent with the indicated assignments. The Fe- -Fe distance of 3.00 Å is consistent with a bridged binuclear iron center in the enzyme. Due to the presence of short Fe-O(tyrosine) linkages at 1.8-1.9 Å, direct evidence for a bridging oxo group at ca. 1.8 Å could not be obtained. The observed Fe-P distance of 3.06 Å is most consistent with the presence of a phosphate as a monodentate ligand to one iron atom in the purple (oxidized) form of the enzyme.
|Original language||English (US)|
|Number of pages||5|
|State||Published - 1986|
ASJC Scopus subject areas
- Inorganic Chemistry