tetrahydrobiopterin
tet·ra·hy·dro·bi·op·ter·in (BH4) (BH4) (tet″rə-hi″dro-bi-opґtər-in) a reduced form of dihydrobiopterin that functions as a coenzyme in the reactions hydroxylating phenylalanine, tryptophan, and tyrosine by carrying electrons to oxygen. Defects in the biosynthesis or regeneration of the coenzyme affect all three hydroxylation reactions, interfere with production of the corresponding neurotransmitter precursors, and result in hyperphenylalaninemia unresponsive to a low-phenylalanine diet unless the missing neurotransmitters can also be supplied; see also tetrahydrobiopterin deficiency, under deficiency.
Medical dictionary.
2011.