Under prolonged X-ray irradiation, the ferrous heme of nitrosylated human adult hemoglobin derivative (HbNO) undergoes a reversible transition generating a 5-coordinate species, due to release of the Fe-NO bond. The overall process can be investigated using X-ray absorption near edge structure ()CANES) spectroscopy. In this work, Fe K-edge XANES spectra were measured at T < 15 K, pH 9.2, i.e., on a high-affinity state (R-HbNO) where all the hemes are 6-coordinate, and at pH 6.5 in the presence of inositol hexakis-phosphate (IHP), i.e., on a low-affinity ligated state (T-HbNO) where the iron-hemes of the alpha-chains are 5-coordinate due to breaking of the Fe-proximal histidine bond. Under X-ray irradiation, 5-coordinate Fe-hemes are populated in both R-HbNO and T-HbNO, the Fe-NO bond lysis induced in T-HbNO involving rebinding of the proximal histidine to the transiently populated 4-coordinate hemes of the alpha-chains. A detailed analysis of the spectra confirms that different intermediate states in the ligand binding cooperative process of hemoglobin can be populated by X-ray irradiation, and that the part of the energy associated to the R-T quaternary transition, that is transmitted to the heme site, can be monitored by XANES spectroscopy.

Ligand Binding Intermediates of Nitrosylated Human Hemoglobin Induced at Low Temperature by X-ray Irradiation

DELLA LONGA, STEFANO
2011-01-01

Abstract

Under prolonged X-ray irradiation, the ferrous heme of nitrosylated human adult hemoglobin derivative (HbNO) undergoes a reversible transition generating a 5-coordinate species, due to release of the Fe-NO bond. The overall process can be investigated using X-ray absorption near edge structure ()CANES) spectroscopy. In this work, Fe K-edge XANES spectra were measured at T < 15 K, pH 9.2, i.e., on a high-affinity state (R-HbNO) where all the hemes are 6-coordinate, and at pH 6.5 in the presence of inositol hexakis-phosphate (IHP), i.e., on a low-affinity ligated state (T-HbNO) where the iron-hemes of the alpha-chains are 5-coordinate due to breaking of the Fe-proximal histidine bond. Under X-ray irradiation, 5-coordinate Fe-hemes are populated in both R-HbNO and T-HbNO, the Fe-NO bond lysis induced in T-HbNO involving rebinding of the proximal histidine to the transiently populated 4-coordinate hemes of the alpha-chains. A detailed analysis of the spectra confirms that different intermediate states in the ligand binding cooperative process of hemoglobin can be populated by X-ray irradiation, and that the part of the energy associated to the R-T quaternary transition, that is transmitted to the heme site, can be monitored by XANES spectroscopy.
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11697/16384
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