2.6. Thiosulfate:Cyanide Sulfurtransferase Activity Assay

The activity on Reaction 1 was measured using a colorimetric assay method described previously [31]. The reaction mixture (250 µL) contained 1 mM~300 mM thiosulfate, 1 mM~300 mM potassium cyanide, and 0.5 µg rhodanese in 300 mM HEPES, pH 7.4. The reaction was performed at room temperature for 5 min and was quenched by adding 250 µL 15% (w/v) formaldehyde, followed by addition of 500 µL ferric nitrate solution (165 mM ferric nitrate monahydrate, 13.3% (v/v) nitric acid). The absorbance of the resulting ferric thiocyanate complex was measured at 460 nm. The concentration of thiocyanate was determined using a standard curve.