Transient Catalytic Voltammetry of Sulfite Oxidase Reveals Rate Limiting Conformational Changes

Abstract : Sulfite oxidases are metalloenzymes that oxidize sulfite to sulfate at a molybdenum active site. In vertebrate sulfite oxidases, the electrons generated at the Mo center are transferred to an external electron acceptor via a heme domain, which can adopt two conformations: a " closed " conformation, suitable for internal electron transfer, and an " open " conformation suitable for intermolecular electron transfer. This conformational change is an integral part of the catalytic cycle. Sulfite oxidases have been wired to electrode surfaces, but their immobilization lead to a significant decrease in their catalytic activity, raising the question of the occurrence of the conformational change when the enzyme is on an electrode. We recorded and quantitatively modelled for the first time the transient response of the catalytic cycle of human sulfite oxidase immobilized on an electrode. We show that conformational changes still occur on the 1 electrode, but at a lower rate than in solution, which is the reason for the decrease in activity of sulfite oxidases upon immobilization.
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Ting Zeng, Silke Leimkuhler, Ulla Wollenberger, Vincent Fourmond. Transient Catalytic Voltammetry of Sulfite Oxidase Reveals Rate Limiting Conformational Changes. Journal of the American Chemical Society, American Chemical Society, 2017, 139 (33), pp.11559-11567. ⟨10.1021/jacs.7b05480⟩. ⟨hal-01614177⟩

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