Short circuiting a sulfite oxidising enzyme with direct electrochemistry: Active site substitutions and their effect on catalysis and electron transfer

► Arg-55 and His-57 play a crucial role in SDH catalysis. ► Loss of positive charge in SDHR55M lowers heme potential by 40 mV. ► SDHWT electrochemical catalysis bypasses higher potential heme cofactor. ► Unusual waveforms indicate potential dependent electron transfer pathway.