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 time it was shown that not all vitamins are amines, the word was already ubiquitous. In 1920, Jack Cecil Drummond proposed that the final "e" be dropped to deemphasize the "amine" reference, after researchers began to suspect that not all "vitamines" (in particular, vitamin A) have an amine component. In 1930, Paul Karrer elucidated the correct structure for beta-carotene, the main precursor of vitamin A, and identified other carotenoids. Karrer and Norman Haworth confirmed Albert Szent-Györgyi's discovery of ascorbic acid and made significant contributions to the chemistry of flavins, which led to the identification of lactoflavin. For their investigations on