Metabolic routes for the three amino acids needed for GSH biosynthesis are outlined and color coded by amino acid provision pathways: yellow, cysteine, denotes intimate crosstalk with methionine metabolism (Lu and Mato, 2012; Zhang et al., 2005); green, glycine, is directly linked to carbohydrate, serine, and choline levels (Locasale, 2013); blue, glutamine/glutamate, indicates coordination with proline and TCA cycle metabolites (Daye and Wellen, 2012). Although not illustrated, one carbon metabolism links glycine metabolism and methionine salvage pathways.