The enzyme is composed of two parts, a glutaminase (PabA in Escherichia coli) and an aminotransferase (PabB). In the absence of PabA and glutamine (but in the presence of Mg2+), PabB can convert ammonia and chorismate into 4-amino-4-deoxychorismate. PabA converts glutamine into glutamate only in the presence of stoichiometric amounts of PabB. In many organisms, including plants, the genes encoding the two proteins have fused to encode a single bifunctional protein. This enzyme is coupled with EC 22.214.171.124
, aminodeoxychorismate lyase, to form 4-aminobenzoate. cf. EC 126.96.36.199
, 4-amino-4-deoxychorismate synthase (2-amino-4-deoxychorismate-forming).