Comment on “Sensitive marker bands for the detection of spin states of heme in surface-enhanced resonance Raman scattering spectra of metmyoglobin” by Y. Kitahama, M. Egashira, T. Suzuki, I. Tanabe and Y. Ozaki

Abstract

We contrast recently reported surface-enhanced resonance Raman spectra (SERRS) of myoglobin on silver nanoparticles with established knowledge about this complex. We conclude that the detected bands are not related to the spin states of the protein cofactor, being rather originated by a heme coordination change induced by the metal surface.

Surface-enhanced resonance Raman scattering of hemoproteins and those in complicated biological systems

“…However, it has been commented that the heme in met-Mb on citratereduced Ag takes a non-native form through detachment from the heme pocket in the protein. 79 Indeed, the SE(R)RS peak (ν 3 ) at 1490 cm −1 , which is assigned to non-native 5cHS, appeared with Soret band excitation. 34,35 On the other hand, the ν 3 peak of met-Mb was observed at 1510 cm −1 , which is assigned to native 6cLS, in the SE(R)RS spectra with excitation at 514 nm by the addition of imidazole and NaN 3 (see Fig.…”

Reply to the comment on “Sensitive marker bands for the detection of spin states of heme in surface-enhanced resonance Raman scattering spectra of metmyoglobin”

“…Feis and Smulevich have commented that the heme in met-Mb on the citrate-reduced Ag becomes the non-native form through detachment from the heme pocket in the protein. 1 Indeed, the SERRS peak was observed at 1490 cm −1 , which is assigned to 5-coordinated heme b in the high spin state, by excitation at 406.7 and 413 nm (Soret band), while the corresponding RRS (ν 3 ) peak of native met-Mb appeared at 1480 and 1510 cm −1 , which is attributed to 6-coordinated heme b in the high and low spin state, respectively. [3][4][5] By the interaction with the Ag surface, conformation of heme c in cytochrome c is changed and is then reflected in the spectra.…”

“…We thank Dr Feis and Prof. Smulevich for their fruitful comment regarding our paper. 1 By changing the ligand and pH, which affect the spin state of metmyoglobin (met-Mb), resonance Raman scattering (RRS) and surface-enhanced resonance Raman scattering (SERRS) spectra of met-Mb were measured. 2 In the RRS spectra, the peak that has been used for discrimination between the heme iron in the high or low spin state appeared at 1610 or 1640 cm −1 , respectively, although the corresponding SERRS peak was barely observed.…”