title: The C-6 proton of tetrahydrobiopterin is acquired from water, not NADPH, during de novo biosynthesis.
abstract: Tetrahydrobiopterin, the cofactor for the aromatic amino acid hydroxylases, is synthesized in mammals from GTP via a pathway involving both dihydropterin and tetrahydropterin intermediates. In this work, we have investigated the mechanism of conversion of the product formed from GTP, 7,8-dihydroneopterin triphosphate, into the tetrahydropterin intermediates. Tetrahydrobiopterin can be oxidized under conditions which yield pterin or pterin 6-carboxylate without exchange of the C-6 and C-7 protons. Using these techniques, a gas chromatography/mass spectrometry method was developed to determine that in the biosynthesis of tetrahydrobiopterin de novo, in preparations of bovine adrenal medulla, the C-6 proton of tetrahydrobiopterin is derived from water and not from NADPH. In contrast, the C-6 proton of tetrahydrobiopterin produced from sepiapterin (6-lactoyl-7,8-dihydropterin) comes from NADPH. The results are consistent with evidence for the formation of the first tetrahydropterin intermediate by a tautomerization without any requirement for NADPH.
authors.forename: G K
authors.initials: GK
authors.lastname: Smith
authors.forename: J A
authors.initials: JA
authors.lastname: Cichetti
authors.forename: P
authors.initials: P
authors.lastname: Chandrasurin
authors.forename: C A
authors.initials: CA
authors.lastname: Nichol
mesh_terms: D000818:Animals; D001708:Biopterins / Q000031:analogs & derivatives / Q000096:biosynthesis*; D002417:Cattle; D003903:Deuterium / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D006160:Guanosine Triphosphate / Q000378:metabolism; D008956:Models, Chemical; D009249:NADP / Q000378:metabolism*; D011522:Protons; D011621:Pteridines / Q000096:biosynthesis*
chemical_list: D011522:Protons; D011621:Pteridines; D001708:Biopterins; D009249:NADP; D006160:Guanosine Triphosphate; D003903:Deuterium; C003402:sapropterin