Using single turnover experiments, we have been able to probe the auto-reduction mechanism of the high-valent iron species in horse heart myoglobin (Mb). Using kinetic solvent isotope effects (sKIE) and proton inventories, we uncovered an unusual transient species that is deuterium dependent. Formation of this transient species produces an unusual inverted sKIE at low pD and normal sKIE at higher pDs. We hypothesized this transient species to be a low barrier hydrogen bond between the distal histidine and the ferryl oxo. Our pD sKIE studies indicate that the formation of this potential transient low barrier hydrogen bond is dependent on the pK<sub>a</sub> of the distal histidine. The spectra of the oxidatively damaged ferric myoglobin also indicates a preference for a specific electron donor or electron transfer pathway that depends on both the pD and the mole ratio of deuterium in the aqueous solvent

Uncovering an unusual transient species in the mechanism of compound II auto-reduction in horse heart myoglobin

ACS Spring 2022

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