Evidence for Conformational and Diffusional Mean Square Displacements in Frozen Aqueous Solution of Oxymyoglobin

Abstract

The temperature dependence of the M\"ossbauer spectra of $^{57}\mathrm{Fe}$ in the active center of oxymyoglobin is analyzed. The effective mean square displacement $〈{x}^{2}〉$ of the iron is a sum of three parts: a vibrational term ${〈{x}^{2}〉}_{v}$, a conformational term ${〈{x}^{2}〉}_{c}$, and a diffusional term ${〈{x}^{2}〉}_{d}$. For $T>240$ K diffusional line broadening $\ensuremath{\Delta}\ensuremath{\Gamma}\ensuremath{\propto}{〈{x}^{2}〉}_{d}$ is observed, along with a decrease in quadrupole splitting due to random reorientation of the electric field gradient.