MYOGLOBINS ULTRAFAST DYNAMICS MEASURED WITH VIBRATIONAL ECHO EXPERIMENTS

Ultrafast infrared (IR) vibrational echo experiments, which are used t o examine the ultrafast dynamics of myoglobin and myoglobin mutants ar e described. Like the NMR spin echo and other NMR pulse sequences, the vibrational echo can extract dynamical and spectroscopic information that cannot be obtained from a vibrational absorption spectrum. The vi brational echo measures the homogenous vibrational linewidth even if t he absorption line is massively inhomogeneously broadened. When combin ed with pump-probe (transient absorption) experiments, the homogeneous pure dephasing (energy level fluctuations) is obtained. Conducting th ese experiments as a function of temperature provides information on d ynamics and intermolecular interactions. The nature of the method and the experimental procedures are outlined. The dynamics of the CO ligan d bound at the active site of the protein myoglobin are examined and c ompared with that in myoglobin mutants. The results provide insights i nto protein dynamics and how protein structural fluctuations are commu nicated to a ligand bound at the active site. (C) 1998 Elsevier Scienc e B.V. All rights reserved.