Determination of Thiosulfate Sulfurtransferase Activity

The activity of TST was determined using Sörbo’s method [49 ] following a procedure used by Wróbel and others [48 (link)]. The reaction mixture consisted of 200 µL of 0.125 M sodium thiosulfate (Sigma-Aldrich, Darmstadt, Germany), 100 µL of 0.2 M potassium dihydrogen phosphate (Sigma-Aldrich, Darmstadt, Germany), 100 µL of homogenates, 100 µL of 38% formaldehyde (only blank sample; Polish Chemicals Reagents, Gliwice, Poland), and 100 µL of 0.25 M potassium cyanide (KCN, Sigma-Aldrich, Darmstadt, Germany). After 5 min incubation at room temperature, the following reagents were added: 100 µL of 38% formaldehyde (only to blank samples) and 500 µL of 0.2 M ferric nitrate reagent (Sigma-Aldrich, Darmstadt, Germany). The amount of thiocyanate formed during the reaction catalyzed with TST was measured colorimetrically at 460 nm. The enzyme units were defined as nmoles of SCN⁻ (thiocyanate), which formed during 1 min incubation per 1 mg of protein.