Enzyme - Magnesium chelatase

Alternative Name(s)
  • Magnesium-chelatase.
  • Mg-chelatase.
  • Mg-protoporphyrin IX magnesio-lyase.
  • Magnesium-protoporphyrin chelatase.
  • Protoporphyrin IX Mg-chelatase.
  • Protoporphyrin IX magnesium-chelatase.
  • Mg-protoporphyrin IX chelatase.
  • Magnesium-protoporphyrin IX chelatase.

Catalytic Activity

ATP + H2O + Mg(2+) + protoporphyrin IX = ADP + 3 H(+) + Mg-protoporphyrin IX + phosphate


There are no Cofactors for this Enzyme

Reaction Mechanism

    Magnesium chelatase has a vital role in chlorophyll biosynthesis, using the energy from ATP hydrolysis to insert a Mg(II) ion into a porphyrin ring. It is part of a generic family of cellular ATPases known as AAA, displaying homology in particular to Cobalt Chelatase. Three subunits make up the overall protein in bacteria, BchI, BChlH and BChlD, also conserved in higher organisms. BChlI has ATPase activity and BChlH binds to the protoporphyrin group while BChlD has an regulatory allosteric role. Currently, there is limited experimental evidence to confirm a formal mechanism of magnesium chelatase with Arg 289 in BChlI being the only identifiable catalytic residue.

    Binding of the porphyrin.BChlH complex and the Magnesium triggers the release of the ATP binding site of the BChI subunit which is able to hydrolyse ATP. The hydrolysis of ATP proceeds via the nucleophilic attack of a water molecule on the gamma phosphate, to form a pentavalent transition state stabilised by Arg 289. This collapses to release the products ADP and Pi, causing subunit motion which results in the transfer of Mg2+ to the porphyrin.
    Catalytic Residues
    AA Uniprot Uniprot Resid PDB PDB Resid
    Arg P26239 289 1g8p 289

Reaction Parameters

  • Kinetic Parameters
    Organism KM Value [mM] Substrate Comment
    Thermosynechococcus vestitus 0.0028 Mg2+ pH 7.7, 45°C
  • Temperature

    There are no reaction parameters information for this Enzyme.

  • pH

    There are no reaction parameters information for this Enzyme.

Associated Proteins

Protein name Organism
Magnesium-chelatase subunit ChlD, chloroplastic Mouse-ear cress
Magnesium-chelatase 30 kDa subunit Rhodobacter capsulatus
Magnesium-chelatase 38 kDa subunit Rhodobacter sphaeroides (strain ATCC 17023 / 2.4.1 / NCIB 8253 / DSM 158)
Magnesium-chelatase subunit ChlI-1, chloroplastic Mouse-ear cress
Magnesium-chelatase subunit ChlI Euglena gracilis