EC 3.5.4.25     
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.
References:
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 3.5.4.25 created 1984, modified 2011]