. "Catalysis of the reaction: GTP + 3 H(2)O = 2,5-diamino-6-hydroxy-4-(5-phosphoribosylamino)-pyrimidine + diphosphate + formate + 3 H(+)." . . "GTP cyclohydrolase II activity" . "GTP 7,8-8,9-dihydrolase (diphosphate-forming)" . "GTP-8-formylhydrolase activity" . "guanosine triphosphate cyclohydrolase II" . . .