STRUCTURAL DYNAMICS OF PROTEINS INVESTIGATED BY HOLE-BURNING SPECTROSCOPY

Low-frequency vibrations in a conformational substate and thermal crossing over conformational barriers have been studied in Zn-substituted and free-base myoglobins by persistent spectral hole-burning. First, in order to investigate the nature of the vibrational modes (or phonons) and the electron-phonon coupling, phonon sideband profiles have been calculated on the basis of a normal-mode analysis for myoglobin, and compared with the observed sideband hole spectra. It has been found that the calculated and the experimental results agree well in the region above 10 cm-1. Next, the distribution of barrier heights between the conformational substates has been obtained by a heat cycle experiment and found to depend on the species that substitute the heme iron and on the presence of a solvent. The primary factor that determines the observed barrier height distributions will be discussed.