Autocatalytic Mechanism in the Anaerobic Reduction of Metmyoglobin by Sulfide Species

PALERMO, JUAN CRUZ; CARLLINNI COLOMBO, MELISA; SEMELAK, JONATHAN A.; SCOCOZZA, MAGALÍ F.; BOUBETA, FERNANDO M.; MURGIDA, DANIEL H.; ESTRIN, DARÍO A.; BARI, SARA E.

INORGANIC CHEMISTRY

AMER CHEMICAL SOC

Año: 2023

0020-1669

The mechanism of the metal centered reduction of metmyoglobin(MbFe III ) by sulfide species (H 2 S/HS − ) under an argon atmosphere has been studiedby a combination of spectroscopic, kinetic, and computational methods. Asymmetric S-shaped time-traces for the formation of MbFe II at varying ratios of excess sulfide wereobserved at pH 5.3 < pH < 8.0 and 25 °C, suggesting an autocatalytic reaction mechanism.An increased rate at more alkaline pHs points to HS − as relevant reactive species for thereduction. The formation of the sulfanyl radical (HS • ) in the slow initial phase wasassessed using the spin-trap phenyl N-tert-butyl nitrone. This radical initiates the formationof S−S reactive species as disulfanuidyl/ disulfanudi-idyl radical anions and disulfide (HSSH •− /HSS •2− and HSS − , respectively). Theautocatalysis has been ascribed to HSS − , formed after HSSH •− /HSS •2− disproportionation, which behaves as a fast reductant towardthe intermediate complex MbFe III (HS − ). We propose a reaction mechanism for the sulfide-mediated reduction of metmyoglobinwhere only ferric heme iron initiates the oxidation of sulfide species. Beside the chemical interest, this insight into the MbFe III /sulfide reaction under an argon atmosphere is relevant for the interpretation of biochemical aspects of ectopic myoglobins found onhypoxic tissues toward reactive sulfur species