Dithionite titrations of wild type, CIS and HRR-Erv forms of TbQSOX. WT TbQSOX in 50 mM phosphate buffer, pH 7.5, containing 1 mM EDTA, was made anaerobic, and titrated at 25 °C with a standardized solution of sodium dithionite yielding curves 1–7. The inset plots the reduction of the oxidase as a function of electron equivalents added per flavin (■) together with comparable titrations with CIS (○) and HRR-Erv (□) proteins.