Picosecond Structural Dynamics of Myoglobin following Photolysis of Carbon Monoxide

We have used picosecond infrared (IR) transient absorption spectroscopy in the amide I band to probe the dynamics of protein motion of myoglobin (Mb) following the photolysis of carbon monoxide. The rise time of the deoxy protein conformation is shown to be about 8 ps. The spectrum of amide I changes was also measured at 50 ps after photolysis and found to be similar to static IR difference spectra and to time-resolved IR spectra taken at times longer than 100 ns. By comparing the results obtained here with other picosecond results on photolysis of CO from Mb, we conclude that the majority of changes seen in the amide I spectra are due to global motion on the proximal side of the heme. The time scale for amide I changes are compared to the results of molecular dynamics calculations.