Reactivity of inorganic sulfide towards ferric hemeproteins.

BARI, SARA ELIZABETH; BIEZA, SILVINA ANDREA; BOUBETA, FERNANDO MARTÍN; PALERMO, JUAN CRUZ; BOECHI, LEONARDO; ESTRIN, DARÍO A.

Iguazú

Simposio; Latinoamerican Symposium on Organometallic Chemistry (6th SiLQCOM 2017)); 2017

The heme moiety is one of the biochemical targets for endogenous hydrogen sulfide, H2S. The outcome of the interaction is diverse, as either the addition to the porphyrin periphery or different metal-centered reactions -and even inertness- have been reported. Our research is focused on essential features of the coordination of inorganic sulfide (H2S/HS-/S2-) to ferric hemeproteins, FeIIIHPs. Microperoxidase 11, FeIIIMP11, a hemepeptide with a histidine as proximal ligand, has been chosen as a model compound. The model is appropriate for the evaluation of the discriminate role of the proximal histidine in the binding. The formation of a moderately stable FeIII-sulfide complex has been observed at pH 6.8. The coordination is not assisted by distal aminoacids, and the affinity is in the lower limit of those measured for sulfide binding FeIIIHPs, As the remarkable affinity of many FeIIIHPs involves stabilization by distal and proximal aminoacids, the affinity of FeIIIMP11 for sulfide represents an estimate for the contribution of the proximal ligand.By measuring the dependence of the binding constant vs. pH, we observed that hydrosulfide, SH-, is the preferred binding species in aqueous environment. Instead, computational evaluations on the speciation of sulfide in the coordination to the hemoglobin I of Lucina pectinata suggest that H2S is the reactive species. These results disclose a role of the environment of the binding site in the selection of the active species.