Increase of the Fe effective charge in hemoproteins during oxygenation process

The x-ray absorption near edge structure (XANES) spectra of hemoglobin and myoglobin have been measured at the wiggler beam line of the Frascati Synchrotron Radiation Facility. The energy shifts of the iron absorption jump edge and the chemical shifts of the bound excited state at threshold of 1s core excitations, going from deoxygenated to oxygenated form, are interpreted as evidence of some increase of the positive effective charge on the iron atom upon oxygenation.