In enzymology, an aminodeoxychorismate synthase (EC 2.6.1.85) is an enzyme that catalyzes the chemical reaction

chorismate + L-glutamine ${\displaystyle \rightleftharpoons }$ 4-amino-4-deoxychorismate + L-glutamate

Thus, the two substrates of this enzyme are chorismate and L-glutamine, whereas its two products are 4-amino-4-deoxychorismate and L-glutamate.^[1][2][3][4]

It is part of a pathway for the biosynthesis of para-aminobenzoic acid (PABA); a precursor for the production of folates. Folates are family of cofactors that are essential for living organisms. Folate cofactors are used in several one-carbon transfer reactions required during the synthesis of essential metabolites, including methionine and thymidylate.^[1]

Aminodeoxychorismate synthase (PabB), a 51 kDa protein in E. coli, is encoded by the gene pabB.^[2] 4-amino-4-deoxychorismate, the product of PabB, can be converted to para-aminobenzoic acid by the enzyme 4-amino-4-deoxychorismate lyase (PabC).

This enzyme belongs to the class of transferases. This means that aminodeoxychorismate synthase catalyzes the transfer of one functional group from a molecule to another. Specifically, aminodeoxychorismate synthase is a transaminase that transfers an amino group to a keto acid. The systematic name is Chorismate:L-glutamine aminotransferase. Formerly aminodeoxychorismate synthase was referred to as PABA synthase; however this name is no longer recommended^[5] as it is understood that the formation of PABA requires the action of a further enzyme (4-amino-4-deoxychorismate lyase).

Common names that the enzyme goes by are:^[6]

• Aminodeoxychorismate synthase
• ADC synthase
• 4-amino-4-deoxychorismate synthase
• PabB

In certain microbial species such as Escherichia coli, aminodeoxychorismate synthase is a heterodimeric complex composed of two proteins, glutamine amidotransferase (PabA) and 4-amino-4-deoxychorismate synthase (PabB). In other species such as plants or lower eukaryotes an enzyme comprising a single polypeptide performs both reactions.

In Escherichia coli, the reaction is a two step process. Glutamine amidotransferase (PabA) and 4-amino-4-deoxychorismate synthase (PabB) form a heterodimeric complex that catalyzes the synthesis of 4-amino-4-deoxychorismate. The first step occurs with PabA abstracting ammonia from glutamine. The second step occurs when PabB reacts both substrates (chorismate and ammonia) to synthesize 4-amino-4-deoxychorismate.

In plants such as Arabidopsis thaliana, aminodeoxychorismate synthase is a monomeric enzyme that carries out both steps of the reaction.^[1]

Aminodeoxychorismate synthase (PabB) is either a heterodimeric or monomeric enzyme depending on what organism it is from. The enzyme has 452-residues and consists of both alpha and beta folds that is very similar to some types of anthranilate synthase. The core of PabB consists of two domains that form a beta sandwich. Also, it has helices and loops around the outside of its core.^[3] The chorismate binding site on PabB consists of amino acids residues that make up beta sheet core and the two key alpha helices.^[4]

Certain aminodeoxychorismate synthase enzymes contain an additional binding site for tryptophan, thought to be a non-functional vestigial binding site. It is believed that aminodeoxychorismate synthase may have evolved from anthranilate synthase (TrpE) - an enzyme that catalyses the production of an intermediate on the path to tryptophan.^[3]

Enzymes with similar structures to aminodeoxychorismate synthase are:

• Anthranilate synthase (TrpE)
• Isochorismate synthase (MenF)
• Salicylate synthase

A common feature among this list of enzymes is that they all utilize chorismate as a substrate.

Aminodeoxychorismate synthase is targeted by the antibiotics atrop-abyssomycin C and 6-fluoroshikimic acid. By inhibiting the production of an intermediate on the pathway to PABA, folate levels are depleted. Without sufficient folate, DNA and protein synthesis are severely impaired.