Reactivity of inorganic sulfide towards ferric hemeproteins.

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

Iguazú

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

The heme moiety is one of the biochemical targets for endogenoushydrogen sulfide, H2S. The outcome of the interaction is diverse, aseither the addition to the porphyrin periphery or different metal-centeredreactions -and even inertness- have been reported. Our research is focused on essential features of the coordination of inorganicsulfide (H2S/HS-/S2-) to ferric hemeproteins,FeIIIHPs. Microperoxidase 11, FeIIIMP11, a hemepeptide with a histidine as proximal ligand, hasbeen chosen as a model compound. The model is appropriate for theevaluation of the discriminate role of the proximal histidine in the binding.The formation of a moderately stable FeIII-sulfidecomplex has been observed at pH 6.8. The coordination is not assisted by distalaminoacids, and the affinity is in the lower limit of those measured forsulfide binding FeIIIHPs, As the remarkable affinity of many FeIIIHPsinvolves stabilization by distal and proximal aminoacids, the affinity of FeIIIMP11 for sulfide represents anestimate for the contribution of the proximal ligand. By measuring the dependence of the bindingconstant vs. pH, we observed that hydrosulfide, SH-, is thepreferred binding species in aqueous environment. Instead, computationalevaluations on the speciation of sulfide in the coordination to the hemoglobinI of Lucina pectinata suggest that H2Sis the reactive species. These results disclose a role of the environment of the binding site in theselection of the active species.