Tetrahydrobiopterin generate BH4 or BH3 radical and BH2, respectively. Research shows that ascorbic acid (also known as ascorbate or vitamin C) can reduce BH3 radical into BH4, preventing the BH3 radical from reacting with other free radicals (superoxide and peroxynitrite specifically). Without this recycling process, uncoupling of the endothelial nitric oxide synthase (eNOS) enzyme and reduced bioavailability of the vasodilator nitric oxide occur, creating a form of endothelial dysfunction. Ascorbic acid is oxidized to dehydroascorbic acid during this process, although it can be recycled back to ascorbic acid. Other than PKU studies, tetrahydrobiopterin has participated in clinical trials studying other approaches
Vitamin B6 pyridoxal and pyridoxamine. Vitamin B was named pyridoxine to indicate its structural homology to pyridine. Vitamin B6 Vitamin B refers to a group of chemically similar compounds which can be interconverted in biological systems. Vitamin B is part of the vitamin B group of essential nutrients. Its active form, pyridoxal 5′-phosphate, serves as a coenzyme in some 100 enzyme reactions in amino acid, glucose, and lipid metabolism. All forms except pyridoxic acid and pyritinol can be interconverted. Absorbed pyridoxamine is converted to PMP by pyridoxal kinase, which is further converted to PLP by pyridoxamine-phosphate transaminase or pyridoxine 5′-phosphate oxidase which