Real time observation of low frequency heme protein vibrations using femtosecond coherence spectroscopy

Femtosecond laser pulses, resonant with the Soret bands of myoglobin (Mb) and cytochrome c, are used to probe coherent low frequency nuclear motion of the heme group. The time domain analysis is in good agreement with frequencies obtained independently using spontaneous resonance Raman spectroscopy. The deoxyMb data reveal a strong oscillation near 300 fs (∼ 100 ${\mathrm{cm}}^{\mathrm{-}1}$) and a persistent feature also appears near 50 ${\mathrm{cm}}^{\mathrm{-}1}$. This is near the frequency expected for heme doming motion, which has been associated with the ligand binding reaction coordinate of Mb.