Fe(III) – Sulfide interaction in globins: Characterization and quest for a putative Fe(IV)-sulfide species

• Published in: Journal of inorganic biochemistry 2018-02, Vol.179, p.32-39
• Main Authors: Mot, Augustin C., Bischin, Cristina, Damian, Grigore, Attia, Amr A.A., Gal, Emese, Dina, Nicoleta, Leopold, Nicolae, Silaghi-Dumitrescu, Radu
• Format: Article
• Language: English
• Subjects: Animals; Cattle; Hemoglobin; Hemoglobins - chemistry; Hexachloroiridate; Horses; Hydrogen sulfide; Hydrogen Sulfide - chemistry; Hydrogen-Ion Concentration; Iron - chemistry; Kinetics; Myocardium - chemistry; Myoglobin; Myoglobin - chemistry; Oxidation-Reduction; Protein adduct; Sulfoferryl
• ISSN: 0162-0134; 1873-3344
• DOI: 10.1016/j.jinorgbio.2017.10.015

The present study reports findings regarding the contrast between H2S interaction with bovine hemoglobin (Hb) and horse heart myoglobin (Mb), in terms of binding and dissociation kinetics, affinities, and mechanism. At pH9.5, oxidation of ferric-sulfide adducts in presence of no free sulfide, using hexachloroiridate as oxidant is examined using stopped-flow UV–vis, EPR, vibrational spectroscopy and mass spectrometry. Oxidation of the ferric-sulfide adduct in such conditions occurs with a putative unstable Fe(IV)-sulfide adduct as intermediate that finally leads to a paramagnetic ferric species with distinct EPR features. As detected by MS spectrometry, this final species appears to be a truncated form of globin at a distinct Tyr. In case of Hb, only β-chain is truncated at Tyr144. Oxidation of sulphide-methemogobin by hexachloroiridate leads to a sulfoferryl species which, unlike the classical ferryl (Compound II, obtained by oxidation of hydroxo-methemoglobin), is very unstable and decomposes to a ferric form with distinct EPR features. The affinity of hemoglobin for sulphide is an order of magnitude than that of myoglobin. [Display omitted] •Kinetic and thermodynamic parameters of H2S-Hb/Mb interaction are strongly pH dependent.•Oxidation of HbFe(III)-SH in alkaline pH occurs with an unstable Fe(IV)=S species.•Fe(IV)=S species leads to a final Hb ferric form with distinct EPR features.•In this final Hb ferric form, β-chains site-specific truncation is observed.