IGPS catalyzes the conversion of PRFAR and glutamine to IGP, AICAR and glutamate. The glutaminase domain produces the ammonia necessary for the cyclase domain to produce IGP and AICAR from PRFAR. The ammonia is channeled to the active site of the cyclase domain. 5-[(5-phospho-1-deoxy-D-ribulos-1-ylimino)methylamino]-1-(5-phospho-beta-D-ribosyl)imidazole-4-carboxamide + L-glutamine = 5-amino-1-(5-phospho-beta-D-ribosyl)imidazole-4-carboxamide + D-erythro-1-(imidazol-4-yl)glycerol 3-phosphate + H(+) + L-glutamate H2O + L-glutamine = L-glutamate + NH4(+) Amino-acid biosynthesis; L-histidine biosynthesis; L-histidine from 5-phospho-alpha-D-ribose 1-diphosphate: step 5/9. In the C-terminal section; belongs to the HisA/HisF family.