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 Structure of Human Glutathione Reductase (PDB ID: 3DK9) (a) Surface Download Scientific Diagram Hydrogen Water vs. Glutathione Reductase (GR): Which Is Better? Evolved H2O Item Scheme showing the enzymatic reactions that catalyze the pyruvate dehydrogenase complex, including pyruvate dehydrogenase activity and diaphorase activity of DLD (A) as well as the glutathione reductase peroxidase activity (B).