Enzyme - Fructose-bisphosphatase

Alternative Name(s)
  • Fructose 1,6-bisphosphatase.
  • Hexose diphosphatase.

Catalytic Activity

beta-D-fructose 1,6-bisphosphate + H2O = beta-D-fructose 6-phosphate + phosphate


There are no Cofactors for this Enzyme

Reaction Mechanism

    Fructose 1,6-bisphosphatase (FBPase) hydrolyses fructose 1,6-bis-phosphate to fructose 6-phosphate and phosphate. The enzyme plays a crucial role in gluconeogenesis, the formation of glucose from non-carbohydrate carbon containing substrates. The enzyme is only capable of catalysing the forward reaction, while phosphofructokinase catalyses the reverse reaction. Regulation of the two enzyme is performed by metabolites such as fructose 2,6 bis-phosphate, ensuring that enhances reactivity of one enzyme is accompanied by suppressed reactivity of the other.

    There are three divalent metal cations present within the catalytic site. Mg(2+) at site one is directly coordinated to the 1-(OH) of the 6 fructose phosphate product as a fifth coordinating ligand. The cation is thought to stabilise the negative charge of the hydroxide group before the transfer of a proton from Asp68, which relays a proton from the substrate neutralises the product. The second metal coordinates to a nucleophilic water molecule, also polarised through hydrogen bonds to Asp74 and Glu98, which abstracts a proton from a second coordinated water. The resulting hydroxide ion is the attacking nucleophile, displacing the 6 fructose phosphate in an SN2 mechanism. The resulting oxide is protonated as stated above.
    Catalytic Residues
    AA Uniprot Uniprot Resid PDB PDB Resid
    Asp P00636 122 1eyi 121
    Glu P00636 98 1eyi 97
    Asp P00636 69 1eyi 68
    Asp P00636 75 1eyi 74
    Asp P00636 119 1eyi 118
    Leu P00636 121 1eyi 120
    Glu P00636 281 1eyi 280
    Glu P00636 99 1eyi 98
    Step Components

    inferred reaction step, native state of enzyme regenerated, proton transfer, overall product formed

    Step 1.

    Asp74 abstracts a proton from the catalytic water, which attacks the metal bound phosphate and eliminates the F6P as a negatively charged intermediate in an SN2-type reaction. It is likely that the reaction proceeds via a pentavalent transition state.

    Step 2.

    Asp68 abstracts the proton from the phosphate group,

    Step 3.

    F6P abstracts the proton from Asp68 to generate the final product.

    Step 4.

    Inferred return step. Asp74 returns a proton to water, which is then transferred to bulk solvent.


    The products of the reaction.

Reaction Parameters

  • Kinetic Parameters
    Organism KM Value [mM] Substrate Comment
    Synechocystis sp. 0.21 D-fructose 1,6-bisphosphate mutant R176A, pH 8.0, 28°C
    Euglena gracilis 0.49 D-fructose 1,6-bisphosphate isozyme EgFBPaseII, pH 8.0, temperature not specified in the publication
    Lactobacillus delbrueckii subsp. lactis 0.6 beta-D-glucose 1,6-bisphosphate mutant enzyme H20A, in 50 mM K+HEPES pH 7.0 at 25°C
    Sulfurisphaera tokodaii 7.2 D-fructose 1,6-bisphosphate pH 7.8, 48°C, mutant enzyme Y348F
    Bacillus methanolicus 8.8 D-fructose 1,6-bisphosphate pH 7.7, 50°
  • Temperature
    Organism Temperature Range Comment
    Clonorchis sinensis 15 - 45 more than 70% of maxiumum activity
    Pisum sativum 30 - 70 30°C: about 40% of maximal activity, 70°C: about 60% of maximal activity
    Thermococcus kodakarensis 37 - 95 the enzyme shows a nearly linear increase in activity between 37°C and 95°C
  • pH
    Organism pH Range Comment
    Pisum sativum 5.5 - 7.5 pH 5.5: about 20% of maximal activity, pH 7.5: about 25% of maximal activity
    Euglena gracilis 6 - 9 activity range, profile overview, recombinant enzyme
    Saccharomyces cerevisiae 6 - 11 pH 6.0: about 25% of maximal activity, pH 11.0.: 55% of maximal activity
    Pelophylax lessonae 6 - 9.5 activity range
    Bos taurus 6.3 - 10 pH 6.3: about 30% of maximal activity, pH 10.0: about 45% of maximal activity

Associated Proteins

Protein name Organism
Fructose-1,6-bisphosphatase 1, chloroplastic Mouse-ear cress
Fructose-1,6-bisphosphatase class 1 Escherichia coli (strain K12)
Fructose-1,6-bisphosphatase 1 class 2 Escherichia coli (strain K12)
Fructose-1,6-bisphosphatase 1 Human
Fructose-1,6-bisphosphatase, chloroplastic Rice