In our SERRS spectra of metmyoglobin by excitation at 514 nm, the peak at 1510 cm⁻¹, which is assigned to the 6-coordinated heme in the low spin state, was observed by the addition of imidazole and NaN₃. Thus, the SERRS likely originates not from the non-native 5-coordinated heme, which is in the high spin state.