HbN and HbO are two truncated hemoglobins from Mycobacterium tuberculosis. Resonance Raman spectra of the deoxy derivatives of these two homodimeric hemoglobins indicate that there is no proximal strain imposed by intersubunit interactions on the proximal iron-histidine bond as that observed in the tetrameric human hemoglobin. In addition, with nanosecond laser flash photolysis, it was concluded that movement along the Fe-His bond following the dissociation of CO does not trigger a quaternary structural transition in these two hemoglobins.