Pathway: tetrahydrobiopterin biosynthesis II

General Background |FRAME: TETRA-H-BIOPTERIN| is a cofactor of several enzymes, including the aromatic amino acid hydroxylases |FRAME: CPLX-7488|, |FRAME: CPLX66-161|, and |FRAME: CPLX-7067| (which are essential for the formation of the neurotransmitters |FRAME: DOPAMINE|, |FRAME: NOREPINEPHRINE|, |FRAME: L-EPINEPHRINE| and |FRAME: SEROTONIN| - see |FRAME: PWY66-301|), all three nitric-oxide synthases (NOS) |FRAME: CPLX-6585|, |FRAME: CPLX-6581|, and |FRAME: CPLX-6582| (see |FRAME: PWY-4983|), and the enzyme |FRAME: CPLX-7489|. In addition, |FRAME: TETRA-H-BIOPTERIN| has been proposed to be involved in promotion of neurotransmitter release in the brain |CITS: [1680529]| and regulation of human melanogenesis |CITS: [8128228]|. Deffciency causes severe neurological disorders characterized by hyperphenylalaninaemia and monoamine neurotransmitter deffciency, and is also implicated in Parkinson's disease, Alzheimer's disease and depression (|CITS: [11592814] [10727395]|. |FRAME: TETRA-H-BIOPTERIN| is present in probably every cell or tissue |CITS: [10727395]|. About This Pathway While most of the |FRAME: TETRA-H-BIOPTERIN| in mammalian cells is probably formed as described in the pathway |FRAME: PWY-5663|, a study performed with rat brains has shown that when the activity of the enzyme |FRAME: CPLX-7490| is limiting, a second pathway can lead to |FRAME: TETRA-H-BIOPTERIN| production |CITS: [2656673]|. In this route, |FRAME: 6-PYRUVOYL-5678-TETRAHYDROPTERIN| is converted by the enzyme |FRAME: MONOMER-13405| to |FRAME: 6-LACTOYL-5678-TETRAHYDROPTERIN|, which is then converted to |FRAME: TETRA-H-BIOPTERIN| by |FRAME: CPLX-7490|.