Part of a heterotetrameric complex that catalyzes the two-step biosynthesis of anthranilate, a precursor for Pseudomonas quinolone signal (2-heptyl-3-hydroxy-4-quinolone; PQS) production which is required to induce the genes for the biosynthesis of the virulence factor pyocyanine (PCN), a characteristic blue-green phenazine pigment produced by P.aeruginosa (PubMed:11591691, PubMed:2153661, PubMed:23449919). In the first step, the glutamine-binding beta subunit (PhnB) of anthranilate synthase (AS) provides the glutamine amidotransferase activity which generates ammonia as a substrate that, along with chorismate, is used in the second step, catalyzed by the large alpha subunit of AS (PhnA) to produce anthranilate (By similarity). chorismate + L-glutamine = anthranilate + H(+) + L-glutamate + pyruvate Secondary metabolite biosynthesis; pyocyanine biosynthesis. Heterotetramer consisting of two non-identical subunits: a beta subunit (PhnB) and a large alpha subunit (PhnA). Single disruption in strain PA04290 results in decreased pyocyanine synthesis (PubMed:2153661). Double phnA-phnB deletions are tryptophan prototrophs; they make less PQS (PubMed:23449919). PhnAB is not feedback inhibited by tryptophan.