Several genes involved in the metabolism of the antioxidant glutathione were found to be upregulated by cadmium exposure, namely the genes encoding the catalytic subunit of glutamate-cysteine ligase (Gclc) that is the rate limiting enzyme in de novo synthesis of glutathione (45); glutathione reductase 1 (Gsr), the reducing enzyme for oxidized glutathione (45); and glutathione-S-transferase, mu 4 (Gstm4), which is a member of the glutathione-S-transferase supergene family of detoxification enzymes (45).