Abstract
AbstractHerein, we report the electrocatalytic voltammetry of holo and heme‐free human sulfite oxidase (HSO) mediated by the synthetic iron complexes 1,2‐bis(1,4,7‐triaza‐1‐cyclononyl)ethane iron(III) bromide, ([Fe(dtne)]Br3.3H2O), potassium ferricyanide (K3[Fe(CN)6]), and ferrocene methanol (FM) at a 5‐(4′‐pyridinyl)‐1,3,4‐oxadiazole‐2‐thiol (Hpyt) modified gold working electrode. Holo HSO contains two electroactive redox cofactors, comprising a mostly negatively charged cyt b5 (heme) domain and a Mo cofactor (Moco) domain (the site of sulfite oxidation), where the surface near the active site is positively charged. We anticipated different catalytic voltammetry based on either repulsive or attractive electrostatic interactions between the holo or heme‐free enzymes and the positively or negatively charged redox mediators. Both holo and heme‐free HSO experimental catalytic voltammetry has been modeled by using electrochemical simulation across a range of sweep rates and concentrations of substrate and both positive and negatively charged electron acceptors ([Fe(dtne)]3+, [Fe(CN)6]3− and FM+), which provides new insights into the kinetics of the HSO catalytic mechanism. These mediator complexes have almost the same redox potential (all lying in the range +415 to +430 mV vs. NHE) and, thus, deliver the same driving force for electron transfer with the Mo cofactor. However, differences in the electrostatic affinities between HSO and the mediator have a significant influence on the electrocatalytic response.
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