Dynamics of the Iron-Containing Core in Crystals of the Iron-Storage Protein, Ferritin, through Mössbauer Spectroscopy

${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ $\gamma$-ray resonance-absorption spectra in crystals of the iron-storage protein, ferritin, display above 265°K, in addition to a normal quadrupole doublet, wide Lorentzian wings extending to velocities of ± 2 cm/sec. The results are interpreted in terms of the dynamics of the iron-containing core of the protein, undergoing bounded diffusive motion within a "cage," characterized by a jump probability per unit time of about 0.5×${10}^8$ ${\sec }^{-1\mathrm{}}$ and a mean-square displacement of about 4.8×${10}^{-2\mathrm{}}$ ${\mathrm{\AA }}^2$ at 298°K.