has role 5,6,7,8-tetrahydrobiopterin 5,6,7,8-tetrahydrobiopterin Beilstein:544742 CHEBI:12074 5,6,7,8-TETRAHYDROBIOPTERIN DrugBank:DB00360 PDBeChem:H4B CHEBI:15372 CHEBI:15219 2-Amino-6-(1,2-dihydroxypropyl)-5,6,7,8-tetrahydoro-4(1H)-pteridinone CAS:17528-72-2 5,6,7,8-Tetrahydrobiopterin Tetrahydrobiopterin chebi_ontology CHEBI:26902 CHEBI:43063 BH4 CHEBI:9480 KEGG:C00272 biopterins coenzyme diol prosthetic group tetrahydropterin nutraceutical human metabolite