Dynamics of Myoglobin−CO with the Proximal Histidine Removed:  Vibrational Echo Experiments

Picosecond infrared vibrational echo measurements from 60 to 300 K on CO bound to the active site of a mutant myoglobin, H93G(N-MeIm), are presented and compared to measurements on native myoglobin and on the mutant H64V. Although in H93G(N-MeIm) (the proximal histidine replaced by glycine, with exogenous N-methylimidazole in the proximal histidine pocket, covalently bound to Fe), the only covalent linkage between heme−CO and the protein is broken, there is no change in the temperature-dependent vibrational pure dephasing time, T 2*. The results demonstrate that severing the only covalent bond between the heme and the globin has little or no effect on the protein dynamics detected by vibration of the CO at the active site of myoglobin.