['Cysteine, a sulfur-containing amino acid, plays an important role in a variety of cellular functions such as protein biosynthesis, methylation, and polyamine and glutathione syntheses. In trypanosomatids, glutathione is conjugated with spermidine to form the specific antioxidant thiol trypanothione (T[SH]2) that plays a central role in maintaining intracellular redox homeostasis and providing defence against oxidative stress.', 'We cloned and characterised genes coding for a cystathionine β-synthase (CβS) and cysteine synthase (CS), key enzymes of the transsulfuration and assimilatory pathways, respectively, from the hemoflagellate protozoan parasite Trypanosoma rangeli.', 'Our results show that T. rangeli CβS (TrCβS), similar to its homologs in T. cruzi, contains the catalytic domain essential for enzymatic activity. Unlike the enzymes in bacteria, plants, and other parasites, T. rangeli CS lacks two of the four lysine residues (Lys26 and Lys184) required for activity. Enzymatic studies using T. rangeli extracts confirmed the absence of CS activity but confirmed the expression of an active CβS. Moreover, CβS biochemical assays revealed that the T. rangeli CβS enzyme also has serine sulfhydrylase activity.'] Is transsulfuration an active pathway for cysteine biosynthesis in Trypanosoma rangeli?