Evolution of Function in the Two Dinucleotide Binding Domains Flavoproteins PLOS Computational Biology File:Glutathione Reductase and Peroxidase Graphic.jpg Wikimedia Commons 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 Harnessing the Mechanism of Glutathione Reductase for Synthesis of Active Site Bound Metallic Nanoparticles and Electrical Connection to Electrodes Journal of the American Chemical Society