Anthranilate synthase (EC:4.1.3.27) catalyses the first step in the biosynthesis of tryptophan. Component I catalyses the formation of anthranilate using ammonia and chorismate. The catalytic site lies in the adjacent region, described in the chorismate binding enzyme family (Pfam:PF00425). This region is involved in feedback inhibition by tryptophan [1]. This family also contains a region of Para-aminobenzoate synthase component I (EC 4.1.3.-).

1: The structures of anthranilate synthase of Serratia marcescens crystallized in the presence of (i) its substrates, chorismate and glutamine, and a product, glutamate, and (ii) its end-product inhibitor, L-tryptophan. Spraggon G, Kim C, Nguyen-Huu X, Yee MC, Yanofsky C, Mills SE; Proc Natl Acad Sci U S A 2001;98:6021-6026. PMID:11371633

2: A metabolic node in action: chorismate-utilizing enzymes in microorganisms. Dosselaere F, Vanderleyden J; Crit Rev Microbiol 2001;27:75-131. PMID:11450855