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.