Reactivity of inorganic sulfide species toward a heme protein model.

BIEZA SA, BOUBETA F, FEIS A, SMULEVICH G, ESTRIN DA, BOECHI L, BARI SE

INORGANIC CHEMISTRY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2015 vol. 54 p. 527 - 533

0020-1669

ABSTRACT: The reactivity of inorganic sulfide speciestoward heme peptides was explored under biorelevantconditions in order to unravel the molecular details of thereactivity of the endogenous hydrogen sulfide toward hemeproteins. Unlike ferric porphyrinates, which are reduced byinorganic sulfide, some heme proteins can form stable Fe III −sulfide adducts. To isolate the protein factors ruling the redoxchemistry, we used as a system model, the undecapeptidemicroperoxidase (MP11), a heme peptide derived fromcytochrome c proteolysis that retains the proximal histidinebound to the Fe III atom. Upon addition of gaseous hydrogensulfide (H 2 S) at pH 6.8, the UV−vis spectra of MP11 closelyresembled those of the low-spin ferric hydroxo complex (onlyattained 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 generalfeatures of a low-spin hexacoordinated heme. Anhydrous sodium sulfide (Na 2 S) was the source of sulfide of choice for the kineticevaluation 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 distalcounterparts, which is significant with regard to the biochemical reactivity of endogenous hydrogen sulfide.