Catalyzes the hydrolysis of the formamide of 2-amino-5-formylamino-6-ribosylamino-4(3H)-pyrimidinone 5'-monophosphate (FAPy) to form 2,5-diamino-6-ribosylamino-4(3H)-pyrimidinone 5'-phosphate (APy). 2-amino-5-formylamino-6-(5-phospho-D-ribosylamino)pyrimidin-4(3H)-one + H2O = 2,5-diamino-6-(1-D-ribosylamino)pyrimidin-4(3H)-one 5'-phosphate + formate + H(+) Requires one Fe(2+) ion for activity. Requires an additional second metal ion that could be Fe(2+) or Zn(2+). Cofactor biosynthesis; coenzyme F420 biosynthesis. Cofactor biosynthesis; riboflavin biosynthesis. Homodimer. Belongs to the creatininase superfamily. FAPy deformylase family.