Fig. 1.

Scheme of transsulfuration pathway (TSP). In mammalians, the amino acid methionine could be converted into homocysteine. Homocysteine could be transformed, through two steps enzymatic reaction, into l-cysteine. l-cysteine acts as a substrate leading to the biosynthesis of three major final products: H₂S, taurine and glutathione. Abbreviation: CAT, cysteine aminotransferase; CBS, cystathionine beta-synthase; CDO cysteine dioxygenase; CSAD, cysteine sulfonic acid decarboxylase; CSE, cystathionine-γ-lyase; GS: glutathione synthase; HDD, hypotaurine dehydrogenase; MPST, 3-mercaptopyruvate sulfurtransferase; γ-GCS: Gamma-glutamylcysteine synthetase.