Reaction catalyzed by 2,5-diamino-6-(5-phospho-D-ribosylamino)pyrimidin-4(3H)-one isomerase/dehydratase (4.2.1.160)

		=			+		H2O
	2,5-diamino-6-(5-phospho-D-ribosylamino)pyrimidin-4(3H)-one	=		7,8-dihydroneopterin 3'-phosphate	+		H2O