The GCLC gene consists of 16 exons and encodes the 636 amino acid protein gamma -GCSc (gamma -glutamylcysteine synthetase heavy subunit), also designated gamma -Lglutamate- L-cysteine ligase catalytic subunit (GLCLC). gamma -GCSc is expressed in hemocytes, brain, liver and kidney. gamma -GCSc associates with a regulatory or modifier subunit, gamma -GCSm (gamma -glutamylcysteine synthetase light subunit), to form a heterodimer, gamma -GCS. gamma -GCS is the first enzyme involved and the rate determining step in glutathione iosynthesis. Oxidants, cadium and methyl mercury upregulate the transcription of gamma -GCS. H2O2 regulation depends on the Yap1 protein and the presence of glutamate, glutamine and lysine. Cadium regulates transcription through proteins Met-4, Met-31 and Met-32. Cbf1, a DNA binding protein, inhibits transcription of gamma -GCS.