The C-6 proton of tetrahydrobiopterin is acquired from water, not NADPH, during de novo biosynthesis.
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.[1]References
- The C-6 proton of tetrahydrobiopterin is acquired from water, not NADPH, during de novo biosynthesis. Smith, G.K., Cichetti, J.A., Chandrasurin, P., Nichol, C.A. J. Biol. Chem. (1985) [Pubmed]
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