Enzyme

3.5.1.38 - Glutamin-(asparagin-)ase

Alternative Name(s)
  • L-ASNase/L-GLNase.
  • L-asparagine/L-glutamine amidohydrolase.
  • Glutaminase-asparaginase.

Catalytic Activity

H2O + L-asparagine = L-aspartate + NH4(+)

Cofactors

There are no Cofactors for this Enzyme

Reaction Mechanism

    glutamin-(asparagin-)ase By Reference

    Glutaminase-asparaginase catalyses the hydrolysis of D and L isomers of glutamine and asparagine.

    Glutaminase-asparaginase belongs to a family of related amidohydrolases, in a less specific class that catalyses the hydrolysis of glutamine to glutamic acid and asparagine to aspartic acid with similar efficiency. They are mechanistically similar to trypsin.

    Tyr 1034 is polarised by Glu 3294 B and facilitates proton abstraction from Thr 1020 and its transfer to the substrate. Nucleophilic attack by Thr 1020 proceeds on the carbonyl carbon and this forms a tetrahedral intermediate, which collapses using Tyr 1034 as a general acid/base catalyst, and activation by Glu 3294 B with release of ammonia as a by-product. Hydrolysis occurs using Thr 1100 to activate water as a nucleophile to attack the carbonyl carbon, which is activated by Tyr 1034. By general acid/base catalysis of Tyr 1034 and activation by Glu 3294 B the tetrahedral intermediate again collapses to break the acyl-enzyme linkage and release the product.
    Catalytic Residues
    AA Uniprot Uniprot Resid PDB PDB Resid
    Glu P10182 294 1djo 287
    Thr P10182 20 1djo 13
    Tyr P10182 34 1djo 27
    Thr P10182 100 1djo 93
    Asp P10182 101 1djo 94
    Lys P10182 173 1djo 166
    Step Components

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

    Step 1.

    Glu3294B deprotonates Tyr1034, which in turn deprotonates Thr1020. Thr1020 then initiates a nucleophilic attack upon the amide carbon of L-asparagine in an addition reaction. The oxyanion formed deprotonates Glu3294B.

    Step 2.

    Glu1294B deprotonates the hydroxyl formed from the oxyanion, initiating the elimination of ammonia, which gains a proton from Glu1294B.

    Step 3.

    The Asp-Lys-Thr triad activates water, which initiates a nucleophilic attack on the carbonyl carbon of the covalently attached intermediate. The formed oxyanion deprotonates the water which attacked.

    Step 4.

    Glu1294B deprotonates the hydroxyl formed from the oxyanion, initiating the elimination of Thr1020, which in turn deprotonates Tyr1034, which then deprotonates Glu1294B.

    Products.

    The products of the reaction.

Reaction Parameters

  • Kinetic Parameters
    Organism KM Value [mM] Substrate Comment
    Achromobacter sp. 0.002 L-glutamine
    Aspergillus niger 0.0026 L-asparagine pH6, 40°C
    Pseudomonas sp. 0.004 L-asparagine
    Delftia acidovorans 0.015 L-asparagine
    Citrobacter freundii 0.029 L-asparagine asparaginase A
  • Temperature
    Organism Temperature Range Comment
    Aspergillus niger 30 - 80
    Tilachlidium humicola 37 - 55
  • pH
    Organism pH Range Comment
    Aspergillus niger 4 - 9
    Rhodotorula toruloides 5 - 7 optimal range for asparaginase activity
    Streptomyces canarius 5 - 11
    Pseudomonas sp. 6 - 9
    Achromobacter sp. 6 - 9

Associated Proteins

Protein name Organism
Glutaminase-asparaginase Pseudomonas fluorescens biotype A
Putative asparaginase/glutaminase Paraburkholderia xenovorans (strain LB400)
L-asparaginase II, putative Castor bean
Glutaminase-asparaginase (Amidohydrolase) Cupriavidus necator (strain ATCC 17699 / H16 / DSM 428 / Stanier 337)
Glutaminase-asparaginase domain protein Acinetobacter baumannii 754286

Citations