title: Reactivity of inorganic sulfide species toward a heme protein model.
abstract: The reactivity of inorganic sulfide species toward heme peptides was explored under biorelevant conditions in order to unravel the molecular details of the reactivity of the endogenous hydrogen sulfide toward heme proteins. Unlike ferric porphyrinates, which are reduced by inorganic sulfide, some heme proteins can form stable Fe(III)-sulfide adducts. To isolate the protein factors ruling the redox chemistry, we used as a system model, the undecapeptide microperoxidase (MP11), a heme peptide derived from cytochrome c proteolysis that retains the proximal histidine bound to the Fe(III) atom. Upon addition of gaseous hydrogen sulfide (H2S) at pH 6.8, the UV-vis spectra of MP11 closely resembled those of the low-spin ferric hydroxo complex (only attained at an alkaline pH) and cysteine or alkylthiol derivatives, suggesting that the Fe(III) reduction was prevented. The low-frequency region of the resonance Raman spectrum revealed the presence of an Fe(III)-S band at 366 cm(-1) and the general features of a low-spin hexacoordinated heme. Anhydrous sodium sulfide (Na2S) was the source of sulfide of choice for the kinetic evaluation of the process. Theoretical calculations showed no distal stabilization mechanisms for bound sulfide species in MP11, highlighting a key role of the proximal histidine for the stabilization of the Fe(III)-S adducts of heme compounds devoid of distal counterparts, which is significant with regard to the biochemical reactivity of endogenous hydrogen sulfide.
authors.affiliation: Departamento de Química Inorgánica, Analítica y Química Física/INQUIMAE-CONICET, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires Ciudad Universitaria , Buenos Aires C1428EHA, Argentina.
authors.forename: Silvina A
authors.initials: SA
authors.lastname: Bieza
authors.forename: Fernando
authors.initials: F
authors.lastname: Boubeta
authors.forename: Alessandro
authors.initials: A
authors.lastname: Feis
authors.forename: Giulietta
authors.initials: G
authors.lastname: Smulevich
authors.forename: Darío A
authors.initials: DA
authors.lastname: Estrin
authors.forename: Leonardo
authors.initials: L
authors.lastname: Boechi
authors.forename: Sara E
authors.initials: SE
authors.lastname: Bari
mesh_terms: D006420:Hemeproteins / Q000737:chemistry / Q000378:metabolism*; D006862:Hydrogen Sulfide / Q000378:metabolism*; D056004:Molecular Dynamics Simulation; D009842:Oligopeptides / Q000737:chemistry / Q000378:metabolism; D010544:Peroxidases / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011487:Protein Conformation; D013440:Sulfides / Q000378:metabolism*
chemical_list: D006420:Hemeproteins; D009842:Oligopeptides; D013440:Sulfides; D010544:Peroxidases; C021799:microperoxidase; C033479:sodium sulfide; D006862:Hydrogen Sulfide