NO binding to horse heart cytochrome c (hhcyt c) has been investigated as a function of pH by both optical absorption and EPR spectroscopies. Lowering pH from 3.5 to 1.5 induces: (i) a blue-shift of the maximum of the optical absorption spectrum in the Soret region from 415 to about 404 nm, and (ii) the appearance of a strong three hyperfine splitting in the gz region of the EPR spectrum. Both spectroscopic features indicate the cleavage of the proximal His18-Fe(II)-NO bond giving rise to the five-coordinated Fe(II)-NO species. By quantification of the relative weight for the six- and the five-coordinated component in the EPR spectra, the pKa value was determined. The apparent pKa of the proximal His N & epsilon; atom (1.8 & PLUSMN; 0.1) is unusually low for a ferrous nitrosylated form since in all investigated ferrous NO-bound heme-proteins the pKa value for the cleavage of the proximal His-Fe (II) bond ranges between 3.7 and 5.8. The pKa value of ferrous nitrosylated hhcyt c indicates that the strength of the proximal His18-Fe(II) bond (= 27.9 kJ/mol) is about 10-22 kJ/mol higher than that observed in all investigated heme-proteins. The strong coordination of the heme-Fe atom by His18 is extremely important to maintain the redox efficiency of cyt c and to keep apoptosis under control. This is a crucial point in tissues, such as retina, where apoptosis might trigger macular degenerative processes.

De Simone, G., Monaca, S.d., Fattibene, P., Bocedi, A., Coletta, M., Ascenzi, P. (2023). Ferrous nitrosylated cytochrome c: the unusual strength of the proximal His18-Fe bond. JOURNAL OF INORGANIC BIOCHEMISTRY, 247 [10.1016/j.jinorgbio.2023.112338].

Ferrous nitrosylated cytochrome c: the unusual strength of the proximal His18-Fe bond

Bocedi, Alessio;
2023-10-01

Abstract

NO binding to horse heart cytochrome c (hhcyt c) has been investigated as a function of pH by both optical absorption and EPR spectroscopies. Lowering pH from 3.5 to 1.5 induces: (i) a blue-shift of the maximum of the optical absorption spectrum in the Soret region from 415 to about 404 nm, and (ii) the appearance of a strong three hyperfine splitting in the gz region of the EPR spectrum. Both spectroscopic features indicate the cleavage of the proximal His18-Fe(II)-NO bond giving rise to the five-coordinated Fe(II)-NO species. By quantification of the relative weight for the six- and the five-coordinated component in the EPR spectra, the pKa value was determined. The apparent pKa of the proximal His N & epsilon; atom (1.8 & PLUSMN; 0.1) is unusually low for a ferrous nitrosylated form since in all investigated ferrous NO-bound heme-proteins the pKa value for the cleavage of the proximal His-Fe (II) bond ranges between 3.7 and 5.8. The pKa value of ferrous nitrosylated hhcyt c indicates that the strength of the proximal His18-Fe(II) bond (= 27.9 kJ/mol) is about 10-22 kJ/mol higher than that observed in all investigated heme-proteins. The strong coordination of the heme-Fe atom by His18 is extremely important to maintain the redox efficiency of cyt c and to keep apoptosis under control. This is a crucial point in tissues, such as retina, where apoptosis might trigger macular degenerative processes.
ott-2023
Pubblicato
Rilevanza internazionale
Articolo
Esperti anonimi
Settore BIO/10
English
Cleavage of the proximal His18-Fe bond
Cytochrome c
EPR spectroscopy
Ferrous nitrosylated cytochrome c
Optical absorption spectroscopy
pH effect
De Simone, G., Monaca, S.d., Fattibene, P., Bocedi, A., Coletta, M., Ascenzi, P. (2023). Ferrous nitrosylated cytochrome c: the unusual strength of the proximal His18-Fe bond. JOURNAL OF INORGANIC BIOCHEMISTRY, 247 [10.1016/j.jinorgbio.2023.112338].
De Simone, G; Monaca, Sd; Fattibene, P; Bocedi, A; Coletta, M; Ascenzi, P
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/2108/337924
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