In some organisms, this enzyme is part of a multifunctional protein, together with one or more other components of the system for the biosynthesis of tryptophan [EC
2.4.2.18 (anthranilate phosphoribosyltransferase ), EC
4.1.1.48 (indole-3-glycerol-phosphate synthase), EC
4.2.1.20 (tryptophan synthase) and EC
5.3.1.24 (phosphoribosylanthranilate isomerase)]. The native enzyme in the complex uses either glutamine or, less efficiently, NH3. The enzyme separated from the complex uses NH3 only.