Ultrafast protein dynamics of hemoglobin as studied by picosecond time-resolved resonance Raman spectroscopy

► We closely examined the temporal behavior of time-resolved resonance Raman spectra of human adult hemoglobin (HbA) and its isolated chains. ► The iron-histidine stretching [ν(Fe-His)] frequency showed a downshift of 2 cm−1 with a time constant of ∼300 ps for HbA and the isolated chains. ► The 2-cm−1ν(Fe-His) downshift in picosecond region seems characteristic to the globin-folded protein with penta-coordinated structure. ► It is suggested that the primary metastable form has more disordered orientation of propionates and less strained environment than the deoxy form. ► The present study showed that HbA adopts the metastable structure within a few picoseconds and remains little changed in the subnanosecond regime.