Folate cofactors are used in several one-carbon transfer reactions required during the synthesis of essential metabolites, including methionine and thymidylate.

In other species such as plants or lower eukaryotes an enzyme comprising a single polypeptide performs both reactions.

Glutamine amidotransferase (PabA) and 4-amino-4-deoxychorismate synthase (PabB) form a heterodimeric complex that catalyzes the synthesis of 4-amino-4-deoxychorismate.

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

[3] The chorismate binding site on PabB consists of amino acids residues that make up beta sheet core and the two key alpha helices.