An X-ray Absorption Study of the Binuclear Iron Center in Deoxyhemerythrin

New EXAFS data at 80 K obtained on deoxyhemerythrin in solution reveal an iron-iron peak at a separation of 3.13 ± 0.03 Á. A repeat of measurements at 300 K shows the iron-iron peak greatly reduced, confirming the hyopthesis of increased relative thermal motion of the two iron atoms from the loss of the μ-oxo bridge. The signal from the first shell of ligands around the iron atoms was analyzed by using a difference spectrum vs. oxyhemerythrin, since rearrangements were expected in only a few ligands. The results of this analysis show that the nine ligands between the irons and the protein remain unchanged, the bound dioxygen is replaced by hydroxide, and the short bond to the bridging oxygen is broken, leaving it bound to one iron. Thus, one iron becomes five-coordinate while the other remains six-coordinate. Details of this analysis are given and the results discussed in light of the information available form other sources.