label: GTP cyclohydrolase IV activity
label_lc: gtp cyclohydrolase iv activity
description: "Catalysis of the reaction: GTP + H2O = 7,8-dihydroneopterin 2',3'-cyclic phosphate + diphosphate + formate + H+. This activity is part of the biosynthesis of methanopterin in Archaea, and requires Fe2+."