2-formamido-N(1)-(5-O-phospho-beta-D-ribosyl)acetamidine + ATP = 5-amino-1-(5-phospho-beta-D-ribosyl)imidazole + ADP + H(+) + phosphate Purine metabolism; IMP biosynthesis via de novo pathway; 5-amino-1-(5-phospho-D-ribosyl)imidazole from N(2)-formyl-N(1)-(5-phospho-D-ribosyl)glycinamide: step 2/2. Belongs to the AIR synthase family. Extended N-terminus.