Enzyme - Inositol-1,4-bisphosphate 1-phosphatase

Alternative Name(s)
  • Inositol polyphosphate 1-phosphatase.

Catalytic Activity

1D-myo-inositol 1,4-bisphosphate + H2O = 1D-myo-inositol 4-phosphate + phosphate


There are no Cofactors for this Enzyme

Reaction Mechanism

    Inositol polyphosphate 1 -phosphatase (l-ptase) removes the l-position phosphate from inositol 1,4-bisphosphate, yielding inositol 4-phosphate. l-Ptase is a ubiquitous monomeric enzyme that requires Mg2+ for activity and is potently inhibited by Li+, leading to its use in therapeutic targets of lithium treatment for manic-depressive illnesses.

    As with most phosphatases the mechanism involves nucleophilic attack on the phosphate group. The nucleophile is an activated water molecule, which is co-ordinated to two magnesium cofactors and then activated by Thr158. This attacks the phosphate group forming a trigonal bipyramidal intermediate which is stabilised by the magnesium ions, break down of this leads to the the inositol 4-phosphate.
    Catalytic Residues
    AA Uniprot Uniprot Resid PDB PDB Resid
    Glu P21327 79 1inp 79
    Asp P21327 54 1inp 54
    Asp P21327 153 1inp 153
    Asp P21327 156 1inp 156
    Asp P21327 317 1inp 317
    Ile P21327 155 1inp 155
    Thr P21327 158 1inp 158
    Step Components

    overall reactant used, proton transfer, overall product formed, unimolecular elimination by the conjugate base, bimolecular nucleophilic addition, native state of enzyme regenerated, inferred reaction step, proton relay

    Step 1.

    The Asp54/Thr158 network deprotonates a water molecule activating it for nucleophilic attack on the phosphate. The penta-covalent intermediate formed is stabilized by the magnesium ions.

    Step 2.

    The intermediate collapses yielding inositol 4-phosphate.

    Step 3.

    Inferred step- product is protonated and the enzyme is regenerated in its native state.


    The products of the reaction.

Reaction Parameters

There are no kinetic parameters information for this Enzyme

Associated Proteins

Protein name Organism
Inositol polyphosphate 1-phosphatase Human
Probable SAL3 phosphatase Mouse-ear cress
SAL2 phosphatase Mouse-ear cress
SAL1 phosphatase Mouse-ear cress
Probable SAL4 phosphatase Mouse-ear cress