James F. Christian

Femtosecond spectroscopy of heme proteins

The technique of femtosecond coherence spectroscopy is applied to the heme proteins myoglobin (Mb) and hemoglobin (Hb). Studies of field driven coherences lead to power spectra that are in good agreement with resonance Raman scattering experiments. Studies of the NO bound derivatives of Mb and Hb reveal rapid photolysis and non-radiative relaxation to the ground electronic state. The ensuing nuclear response is oscillatory and displays strong coupling of the NO photolysis reaction to the iron-histidine vibration and to the heme doming mode, which we locate at approximately 40 cm-1. The doming mode was previously assigned to a mode at approximately 80 cm-1, which we now believe is actually the first overtone of the doming motion. Other modes at approximately 120 cm-1 and 160 cm-1 are also exposed by the new data, suggesting that a progression of doming harmonics is excited to the strong coupling of this mode to the photolysis reaction.