The enzyme from Chlorella shows very little activity towards monothiols such as glutathione and cysteine (cf. EC 2.8.1.3 thiosulfate---thiolsulfurtransferase). The enzyme probably transfers the sulfur atom onto one thiol group to form -S-S-, and sulfide is spontaneously expelled from this by reaction with the other thiol group. May be identical with EC 2.8.1.1 thiosulfate sulfurtransferase.