The effect of pH on the X-band electron paramagnetic resonance (EPR) spectrum of ferrous nitrosylated human adult tetrameric hemoglobin (HbNO) as well as of ferrous nitrosylated monomeric alpha- and beta-chains has been investigated, at -163 degrees C. At pH 7.3, the X-band EPR spectrum of tetrameric HbNO and ferrous nitrosylated monomeric alpha- and beta-chains displays a rhombic shape. Lowering the pH from 7.3 to 3.0, tetrameric HbNO and ferrous nitrosylated monomeric alpha- and beta-chains undergo a transition towards a species characterized by a X-band EPR spectrum with a three-line splitting centered at 334 mT. These pH-dependent spectroscopic changes may be taken as indicative of the cleavage, or the severe weakening, of the proximal HisF8-Fe bond. In tetrameric HbNO, the pH-dependent spectroscopic changes depend on the acid-base equilibrium of two apparent ionizing groups with pK(a) values of 5.8 and 3.8. By contrast, the pH-dependent spectroscopic changes occurring in ferrous nitrosylated monomeric alpha- and beta-chains depend on the acid-base equilibrium of one apparent ionizing group with pK(a) values of 4.8 and 4.7, respectively. The different pK(a) values for the proton-linked spectroscopic transition(s) of tetrameric HbNO and ferrous nitrosylated monomeric alpha- and beta-chains suggest that the quaternary assembly drastically affects the strength of the proximal HisF8-Fe bond in both subunits. This probably reflects a 'quaternary effect', i.e., structural changes in both subunits upon tetrameric assembly, which is associated to a relevant variation of functional properties (i.e., proton affinity). (c) 2005 Elsevier Inc. All rights reserved.

Ascenzi, P., Bocedi, A., Fasano, M., Gioia, M., Marini, S., Coletta, M. (2005). Proton-linked subunit heterogeneity in ferrous nitrosylated human adult hemoglobin: an EPR study. JOURNAL OF INORGANIC BIOCHEMISTRY, 99(5), 1255-1259 [10.1016/j.jinorgbio.2005.01.009].

Proton-linked subunit heterogeneity in ferrous nitrosylated human adult hemoglobin: an EPR study

Bocedi, A;GIOIA, MAGDA;MARINI, STEFANO;COLETTA, MASSIMILIANO
2005-01-01

Abstract

The effect of pH on the X-band electron paramagnetic resonance (EPR) spectrum of ferrous nitrosylated human adult tetrameric hemoglobin (HbNO) as well as of ferrous nitrosylated monomeric alpha- and beta-chains has been investigated, at -163 degrees C. At pH 7.3, the X-band EPR spectrum of tetrameric HbNO and ferrous nitrosylated monomeric alpha- and beta-chains displays a rhombic shape. Lowering the pH from 7.3 to 3.0, tetrameric HbNO and ferrous nitrosylated monomeric alpha- and beta-chains undergo a transition towards a species characterized by a X-band EPR spectrum with a three-line splitting centered at 334 mT. These pH-dependent spectroscopic changes may be taken as indicative of the cleavage, or the severe weakening, of the proximal HisF8-Fe bond. In tetrameric HbNO, the pH-dependent spectroscopic changes depend on the acid-base equilibrium of two apparent ionizing groups with pK(a) values of 5.8 and 3.8. By contrast, the pH-dependent spectroscopic changes occurring in ferrous nitrosylated monomeric alpha- and beta-chains depend on the acid-base equilibrium of one apparent ionizing group with pK(a) values of 4.8 and 4.7, respectively. The different pK(a) values for the proton-linked spectroscopic transition(s) of tetrameric HbNO and ferrous nitrosylated monomeric alpha- and beta-chains suggest that the quaternary assembly drastically affects the strength of the proximal HisF8-Fe bond in both subunits. This probably reflects a 'quaternary effect', i.e., structural changes in both subunits upon tetrameric assembly, which is associated to a relevant variation of functional properties (i.e., proton affinity). (c) 2005 Elsevier Inc. All rights reserved.
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Rilevanza internazionale
Articolo
Esperti anonimi
Settore BIO/10
English
Con Impact Factor ISI
ferrous nitrosylated tetrameric human adult hemoglobin; ferrous nitrosylated monomeric alpha- and beta-chains; proton-linked subunit heterogeneity in ferrous nitrosylated human adult tetrameric hemoglobin; EPR spectroscopy
Ascenzi, P., Bocedi, A., Fasano, M., Gioia, M., Marini, S., Coletta, M. (2005). Proton-linked subunit heterogeneity in ferrous nitrosylated human adult hemoglobin: an EPR study. JOURNAL OF INORGANIC BIOCHEMISTRY, 99(5), 1255-1259 [10.1016/j.jinorgbio.2005.01.009].
Ascenzi, P; Bocedi, A; Fasano, M; Gioia, M; Marini, S; Coletta, M
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/29353
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