Cysteine Dioxygenase Type 1 (CDO1) is a mammalian non-heme iron enzyme that belongs to the cysteine dioxygenase family. CDO1 is highly expressed in the liver and placenta, and has a low expression in heart, brain and pancreas. CDO1 can also be detected in hepatoblastoma HepG2 cells. CDO1 catalyzes the conversion of L-cysteine to cysteine sulfinic acid by incorporation of dioxygen. CDO1 is a vital regulator of cellular cysteine concentrations and has an essential role in maintaining the hepatic concentration of intracellular free cysteine within a proper narrow range. CDO1 is able to alter intracellular cysteine levels and glutathione levels.