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Catalytic Site Atlas

CSA LITERATURE entry for 1iph

E.C. namecatalase
SpeciesEscherichia coli (Bacteria)
E.C. Number (IntEnz)
CSA Homologues of 1iphThere are 58 Homologs
CSA Entries With UniProtID P21179
CSA Entries With EC Number
PDBe Entry 1iph
PDBSum Entry 1iph
MACiE Entry 1iph

Literature Report

IntroductionCatalase is a heme containing enzyme which catalyses the breakdown of hydrogen peroxide (H2O2) to water and molecular oxygen. It also has a peroxidase activity where the reduction of H2O2 is accompanied by the oxidation of another compound. Catalase is present in all aerobic cells. Its main function is to protect cells from the toxic effects of hydrogen peroxide. In eukaryotic organisms and in some prokaryotes catalase is a molecule composed of four identical subunits. Each of the subunits binds one protoheme IX group. Catalase HPII from E. Coli is the largest known catalase. A unique covalent bond between the Cb of the essential Tyr415 and the Nd of His392 has been noted.
MechansimThe mechanism proceeds via a two step process. In the first step, the enzyme is oxidised by hydrogen peroxide to an intermediate, Compound I, which in the second stage is reduced back to the original resting state releasing water and molecular oxygen. The total reaction is 2 moles of hydrogen peroxide gives 2 moles of water and one mole of oxygen.
H2O2 enters the active site and binds to the heme Fe, histidine 128, and asparagine 201. The oxygen of H2O2 that is bound to the Fe donates a proton to the NE of histidine 128. Histidine 128 then in turn donates the proton to the other H2O2 oxygen bound to asparagine 201. This leaves water bound to asparagine which can then leave and the oxidised heme iron. A second molecule of hydrogen peroxide enters the active site and there is now an enzyme-compound 1-H2O2 complex, which evolves spontaneously to a compound II-like species in which formally a hydrogen atom has transferred (proton transfer to the oxoferryl oxygen and porphyrin radical of Compound I). In concert with this step a hydrogen atom is donated to His392 forming a positively charged imidazolium ring. This then acts as a general acid and donates it to the iron-bound hydroxide group, which leaves as water. Restoring the enzyme back to it's original state and releasing molecular oxygen and water.

Catalytic Sites for 1iph

Annotated By Reference To The Literature - Site 1 (Perform Site Search)
ResidueChainNumberUniProtKB NumberFunctional PartFunctionTargetDescription
HisA128128macie:sideChainActs as a general base to receive a proton from substrate, which it in turn donates back to form water.
AsnA201201macie:sideChainPolarises the hydrogen peroxide in order for water to leave and the oxygen to remain bound to iron.
HisA392392macie:sideChaincts to receive a proton fro hydrogen peroxide and donated one to the iron-bound hydroxide group to release water.

Literature References

Peretz M
Amino acid sequence of alcohol dehydrogenase from the thermophilic bacterium Thermoanaerobium brockii.
Biochemistry 1989 28 6549-6555
PubMed: 2790012
Loewen PC
Catalase HPII of Escherichia coli catalyzes the conversion of protoheme to cis-heme d.
Biochemistry 1993 32 10159-10164
PubMed: 8399141