IGPS catalyzes the conversion of PRFAR and glutamine to IGP, AICAR and glutamate. The HisF subunit catalyzes the cyclization activity that produces IGP and AICAR from PRFAR using the ammonia provided by the HisH subunit (By similarity). IGP synthase cyclase subunit IGP synthase subunit HisF Imidazole glycerol phosphate synthase subunit HisF SaurJH9_2697 ImGP synthase subunit HisF 252 MIKKRIIPCLDVKDGRVVKGIQFKGLRDIGNPVDLAIYYNEAGADELVFLDISKTEEGHSLMLEVIEQTASRLFIPLTVGGGIQSLDDITQLLNHGADKVSLNSSALKNPQLIKQASDKFGRQCICIAIDSYYDPERKAHYCCTHGGKKMTNIKVYDWVQQVEQLGAGELLVTSMGHDGMKQGFDIEHLAKIKSLVNIPIIASGGGGNAQHFVELFNQTDVSAGLAASILHDRETTVQSIKEVIRQGGIAVR hisF HIS6_STAA9