Hemoglobin iron coordination

Dr. Spijkerman I would be wilhng to have hemoglobin 7-coordinated because we worked on the iron EDTA salts, which show a very asymmetric quadrupole splitting, and they are 7-coordinated. The spectra of hemoglobin and the iron EDTA salts are quite similar. I think that spin-spin relaxation occurs, which is more pronounced with 7-coordination than one would expect for 6 or 4. If this is the case, there might be some indication of it, but the Mossbauer spectrum certainly doesn t indicate it from the chemical shift or quadrupole splitting. 

Hemoglobin proteins comprise 65 percent of the iron (Fe) in the human body. Hemoglobin is a flat planar-shaped molecule that s springy and has a heavy magnet (the iron atom) in the middle. In hemoglobin, iron is coordinated by four nitrogen atoms. 

P. R. Girodot (The University of Texas at Arlington) A recent report stated that hemoglobin contained three globins and not two attached to the central iron atom, as shown by the Sorel eflFect. If so, it would not be octahedral but 7-coordinated. In this case, is there any evidence to support this idea or disprove it from the Mossbauer data presently available ... 

Four of the six coordination sites of the iron in hemoglobin are occupied by the nitrogen atoms of the pyrrol rings, and another is occupied by a histidine residue of the globin (the proximal histidine). The iron s sixth site is coordinated with oxygen in oxyhemoglobin and with H2O in deoxyhemoglobin. 

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