Enzyme - Anthranilate synthase

Alternative Name(s)

There are no alternative names for this Enzyme

Catalytic Activity

horismate + L-glutamine = anthranilate + H(+) + L-glutamate + pyruvate


There are no Cofactors for this Enzyme

Reaction Mechanism

    Anthranilate synthase catalyses the initial reaction in tryptophan biosynthesis in microorganisms and plants. This enzyme is one of a family of glutamine amidotransferases, enzymes that utilise the amide of glutamine in the biosynthesis of amino acids, nucleotides, coenzymes, and an amino sugar. Glutamine amidotransferases thus exert major role in utilisation of assimilated nitrogen. Anthranilate synthase is the most thoroughly characterised glutamine amidotransferase.

    The enzyme from Serratia marcescens is a heterotetramer of anthranilate synthase (TrpE) and glutamine amidotransferase (TrpG) subunits both of which are required for function.

    In the TrpG subunit anthranilate synthase produces anthranilate from chorismate via transfer of an amino group, (generated from glutamine) using a catalytic triad of with well-known mechanism consisting of Cys84, His175, and Glu177. In the second AIDC lyase part of the reaction a standard second-order elimination can be invoked to yield the double bond between C2 and C3 with a histidine (H306) as the base abstracting the C2 proton and pyruvate as the leaving group. Mg(II) and water provide an assisting acid group.
    Catalytic Residues
    AA Uniprot Uniprot Resid PDB PDB Resid
    Leu Q06129 85 1qdl 85
    Gly Q06129 56 1qdl 56
    His Q06128 306 1qdl 307
    Thr Q06128 333 1qdl 334
    Tyr Q06128 357 1qdl 358
    Arg Q06128 377 1qdl 378
    Cys Q06129 84 1qdl 84
    His Q06129 175 1qdl 175
    Gly Q06128 393 1qdl 394
    Glu Q06129 177 1qdl 177
    Step Components

    overall reactant used, proton transfer, unimolecular elimination by the conjugate base, overall product formed, enzyme-substrate complex formation, bimolecular nucleophilic addition, intermediate formation, intermediate terminated, native state of enzyme regenerated, bimolecular elimination, deamination, intermediate collapse, enzyme-substrate complex cleavage

    Step 1.

    His175 deprotonates Cys84, activating it for a nucleophilic attack upon L-glutamine, forming an enzyme-substrate covalent bond.

    Step 2.

    The tetrahedral intermediate collapses, liberating ammonia, which deprotonates His175 and then passes to the other catalytic domain.

    Step 3.

    His175 deprotonates a water molecule, which initiates a nucleophilic attack on the Cys-bound intermediate.

    Step 4.

    The tetrahedral intermediate collapses, liberating Cys84, which deprotonates His175, and the glutamate product.

    Step 5.

    Ammiona acts as a nucleophile, adding to chorismate and eliminating water.

    Step 6.

    His306 deprotonates the C2 of the intermediate, eliminating the anthranilate product with concomitant deprotonation of the His306.


    The products of the reaction.

Reaction Parameters

There are no kinetic parameters information for this Enzyme

Associated Proteins

Protein name Organism
Anthranilate synthase component 1 2 Haloarcula marismortui (strain ATCC 43049 / DSM 3752 / JCM 8966 / VKM B-1809)
Anthranilate synthase, phenazine specific Pseudomonas chlororaphis
Anthranilate synthase component 1 1 Haloarcula marismortui (strain ATCC 43049 / DSM 3752 / JCM 8966 / VKM B-1809)
Probable anthranilate synthase component 1 Fission yeast
Anthranilate synthase component 2 Pseudomonas putida