Simplified scheme of the cysteine metabolism. Dotted lines with empty arrows represent multistep conversions. APS Kinase indicates adenosine 5′-phosphosulfate kinase; CBS, cystathionine-β-synthase; CDO, cysteine dioxygenase; GCL, glutamate cysteine ligase; MPST, mercaptopyruvate sulfurtransferase; PAPS, 3′-phosphoadenosine 5′-phosphosulfate; SO, sulfite oxidase; and TST, thiosulfate sulfurtransferase.