The effect of temperature on the radial distribution function for iron in native horse spleen ferritin

Abstract

Iron K-edge X-ray absorption spectra were recorded for a sample of freeze-dried horse spleen ferritin over a range of temperatures from 40 to 300 K. Gaussian-type radial distribution functions were fitted to the data from all temperatures simultaneously and the obtained mean-square relative displacements σ2 (EXAFS Debye-Waller factors) were fitted using an Einstein model. For iron atoms in the second and/or third coordination shell an Einstein temperature of 330 ± 20 K was obtained. If oxygen was assumed in the second or third shell, its Einstein temperature was 460 ± 20 K. This indicates that the core of ferritin may have a somewhat more rigid structure than those of previously studied ferritin analogues (polysaccharide iron complexes)