Flavin adenine dinucleotide (FAD) activates the glutathione reductase Download Scientific Diagram Reactive Oxygen Species: A Key Constituent in Cancer Survival Glutathione peroxidase 4: a new player in neurodegeneration? Molecular Psychiatry The biochemical pathway that makes BH4 requires GTP as the substrate and three dedicated enzymes (GTP cyclohydrolase I, 6pyruvoyltetrahydropterin synthase, and sepiapterin reductase); the key redox cofactors used in the pathway and Glutathione NADPH + H+ NADP+ FAD Pentose Phosphate Pathway Riboflavin Glutamate (Oxidized glutathione) (Reduced glutathione, a s