On extended x-ray absorption fine structure studies of hemoglobin.

Results of extended x-ray absorption fine structure (EXAFS) studies of the iron atom in deoxygenated hemoglobin are reviewed. It is shown that the iron-porphinato nitrogen distance has been determined to be 2.06 +/- 0.01 A by two independent investigations [Eisenberger, P.M., Shulman, R.G., Kincaid, B. M., Brown, G. S. & Ogawa, S. (1978) Nature (London) 274, 30-34 and Perutz, M.F., Hasnain, S.S., Duke, P.J., Sessler, J.L. & Hahn, J.E. (1982) Nature (London) 295, 535-538]. Difficulties experienced by Perutz et al. in using this distance to calculate the iron's distance above the plane by triangulation are shown to be due to ignoring differences between ferrous and ferric hemes. It is concluded that the iron is 0.2 +/- 0.1 0.2 A above the plane of the nitrogens as originally shown by Eisenberger et al.