Reaction catalyzed by phosphoribosyl-AMP cyclohydrolase (3.5.4.19)

		+		H2O	=
	1-(5-phospho-beta-D-ribosyl)-AMP	+		H2O	=		1-(5-phospho-beta-D-ribosyl)-5-[(5-phospho-beta-D-ribosylamino)methylideneamino]imidazole-4-carboxamide