Manganese peroxidase

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manganese peroxidase
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ExPASy
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In

enzymology, a manganese peroxidase (EC 1.11.1.13) is an enzyme that catalyzes the chemical reaction

2 Mn(II) + 2 H+ + H2O2 2 Mn(III) + 2 H2O

The 3

substrates of this enzyme are Mn(II), H+, and H2O2, whereas its two products are Mn(III) and H2O
.

This enzyme belongs to the family of oxidoreductases, to be specific those acting on a peroxide as acceptor (peroxidases). The systematic name of this enzyme class is Mn(II):hydrogen-peroxide oxidoreductase. Other names in common use include peroxidase-M2, and Mn-dependent (NADH-oxidizing) peroxidase. It employs one cofactor, heme. This enzyme needs Ca2+ for activity.

White rot fungi secrete this enzyme to aid lignin degradation.

Discovery and characterization

Manganese peroxidase (commonly referred to as MnP) was discovered in 1985 simultaneously by the research groups of Michael H. Gold

mold
species has yet been found which naturally produces it.

Reaction mechanism

Sketch of manganese peroxidase mechanism showing the initial state, iron peroxide complex, and Compounds I and II. Here, the heme cofactor is represented via an iron-nitrogen complex. The Fe(IV) oxo-porphyrin radical resonates throughout the heme.

MnP catalysis occurs in a series of irreversible oxidation-reduction (

organic peroxide, enters the active site of MnP. There the oxygen in H2O2 binds to an Fe(III) ion in the heme cofactor to form an iron peroxide complex. Two electrons are transferred from Fe3+ to peroxide, breaking the oxygen-peroxide bond to form H2O and a Fe(IV) oxo-porphyrin radical complex. This oxidized intermediate is known as MnP Compound I. MnP Compound I then binds to a monochelated Mn(II) ion, which donates an electron to quench the radical and form Mn(III) and MnP Compound II, a Fe(IV) oxo-porphyrin complex. MnP Compound II oxidizes another Mn(II) ion to Mn(III) and is reduced by the reaction of two H+ ions and the iron bound oxygen. This reforms the Fe(III) ion in the heme and releases a second water molecule.[5]
There are many deviations from this traditional catalytic cycle. MnP Compound I can be used to oxidize free Mn(II),
aromatic compounds.[6]

Chelators

Mn(III) is unstable in

O2. However, this side reaction has little impact on enzymatic activity because it follows slower third order kinetics.[4]

Structural studies

Structure of manganese peroxidase. Bounded manganese and calcium ions are highlighted in purple and pink, respectively.

As of late 2007, 6

structures have been solved for this class of enzymes, with PDB accession codes 1MN1, 1MN2, 1YYD, 1YYG, 1YZP, and 1YZR
.

Although MnP, like other

acidic residues which are used to stabilize Mn(II) or Mn(III) when it is bound to the enzyme. The specific residues vary between species, but their number and relative location in the folded protein is conserved. There are a total of 357 amino acid residues in the MnP of P. chrysosoporium, and a similar number in enzymes produced by other basidiomycetes.[9]

Biochemical significance

The major function of the Mn(III) ions produced by MnP is oxidation and degradation of lignin.

α-carbon oxidation in phenols.[13]

Regulation

MnP activity is controlled via transcriptional regulation. MnP is up-regulated by increases in extracellular Mn(II)[14] and H2O2 concentrations. It has been found that increased O2 concentration and heat stress also activate MnP.[15]

References

  1. PMID 4062285
    .
  2. doi:10.1111/j.1574-6968.1985.tb00831.x
    .
  3. PMID 2925681
    .
  4. ^
    PMID 1429709
    .
  5. doi:10.1016/S0141-0229(01)00528-2
    .
  6. S2CID 39842460
    .
  7. PMID 9636044
    .
  8. doi:10.1016/0959-440X(92)90230-5
    .
  9. doi:10.1016/S0141-0229(01)00521-X
    .
  10. PMID 3207431
    .
  11. PMID 2760063
    .
  12. S2CID 25335594
    .
  13. PMID 1599925
    .
  14. PMID 2061289
    .
  15. PMID 7887613
    .

Further reading
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