Direct probe of iron vibrations elucidates NO activation of heme proteins.
We use nuclear resonance vibrational spectroscopy (NRVS) to identify the Fe-NO stretching frequency in the NO adduct of myoglobin (MbNO) and in the related six-coordinate porphyrin Fe(TPP)(1-MeIm)(NO). Frequency shifts observed in MbNO Raman spectra upon isotopic substitution of Fe or the nitrosyl nitrogen confirm and extend the NRVS results. In contrast with previous assignments, the Fe-NO frequency of these six-coordinate complexes lies 70-100 cm-1 lower than in the analogous five-coordinate nitrosyl complexes, indicating a significant weakening of the Fe-NO bond in the presence of a trans imidazole ligand. This result supports proposed mechanisms for NO activation of heme proteins and underscores the value of NRVS as a direct probe of metal reactivity in complex biomolecules.
Zeng
Weiqiao
W
Department of Physics and Center for Interdisciplinary Research on Complex Systems, Northeastern University, Boston, Massachusetts 02115, USA.
Silvernail
Nathan J
NJ
Wharton
David C
DC
Georgiev
Georgi Y
GY
Leu
Bogdan M
BM
Scheidt
W Robert
WR
Zhao
Jiyong
J
Sturhahn
Wolfgang
W
Alp
E Ercan
EE
Sage
J Timothy
JT
D006420:Hemeproteins / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D009569:Nitric Oxide / Q000737:chemistry*; D019906:Nuclear Magnetic Resonance, Biomolecular; D014732:Vibration
D006420:Hemeproteins; D009569:Nitric Oxide; D007501:Iron