The irreversible transfer of an amino group from L-glutamine to 5'-phosphoribosylformylglycinamide (FGAR), forming 5'-phosphoribosylformylglycinamidine (FGAM) and glutamate, accompanied by the conversion of ATP to ADP and orthophosphate, is catalyzed by phosphoribosylformylglycinamidine synthetase. The human enzyme has been purified and characterized biochemically (Barnes et al. 1994). Fluoresence microscopy studies of cultured human cells have shown that the enzyme is cytosolic and suggest that it may co-localize with other enzymes of de novo IMP biosynthesis under some metabolic conditions (An et al. 2008).