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

⁵⁷Fe γ-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×{}10⁸ sec^-1 and a mean-square displacement of about 4.8×{}10^-2 ² at 298^∘{}K.