Accepted name: GTP cyclohydrolase II
Reaction: GTP + 3 H2O = formate + 2,5-diamino-6-hydroxy-4-(5-phospho-D-ribosylamino)pyrimidine + diphosphate
Other name(s): guanosine triphosphate cyclohydrolase II; GTP-8-formylhydrolase
Systematic name: GTP 7,8-8,9-dihydrolase (diphosphate-forming)
Comments: Two C-N bonds are hydrolysed, releasing formate, with simultaneous removal of the terminal diphosphate.
1.  Foor, F. and Brown, G.M. Purification and properties of guanosine triphosphate cyclohydrolase II from Escherichia coli. J. Biol. Chem. 250 (1975) 3545–3551. [PMID: 235552]
[EC created 1984, modified 2011]