four steps: the radical-mediated cyclization of nucleotide, guanosine 5'-triphosphate (GTP), to (8S)‑3 ́,8‐cyclo‑7,8‑dihydroguanosine 5 ́‑triphosphate (3 ́,8‑cH2GTP), the formation of cyclic pyranopterin monophosphate (cPMP) from the 3 ́,8‑cH2GTP, the conversion of cPMP into molybdopterin (MPT), the insertion of molybdate into MPT to form Moco (molybdenum cofactor). Tetrahydrobiopterin Tetrahydrobiopterin, the major unconjugated pterin in vertebrates, is involved in three families of enzymes that effect hydroxylation. The aromatic amino acid hydroxylases include phenylalanine hydroxylase, tyrosine hydroxylase, and tryptophan hydroxylases. They are involved in the synthesis of neurotransmitters catecholamine and serotonin. Tetrahydrobiopterin is also required for the functioning of alkylglycerol monooxygenase, whereby monoalkylglycerols are broken down to glycerol and an aldehyde. In the synthesis of nitric oxide the pterin-dependent nitric oxide synthase converts arginine to N-hydroxy derivative, which in turn releases NO. Other pterins Tetrahydromethanopterin is a cofactor in methanogenesis, which is a metabolism adopted by many organisms, as a form of anaerobic respiration. It carries the C1 substrate in the course of the formation or production of methane. It is structurally similar to folate. Pterin pigments Cyanopterin is a glycosylated version of pteridine of unknown function in cyanobacteria. See also Folic acid Molybdopterin Pteridine Tetrahydrobiopterin Tetrahydromethanopterin References External links https://web.archive.org/web/20131202231508/http://grupoargentinodefotobiologia.info/grupos/pteridinas/e_index.html Cofactors Pteridines Enones