Question

Describe how a catalase works. Be specific.

Your answer must include:

• Each step of the reaction
• Coenzyme? Cofactor? Prosthetic group? Ligand?
• Key amino acid residue which is important?

Answer 1

catalase is an enzyme used by our body to protect our cells from oxidative damage by reactive oxygen species (ROS) . It catalyzes the decomposition of hydrogen peroxide(H₂O₂)

REACTION

H₂O₂ + Fe(III)-E ----> H₂O +O=Fe(IV)-E

H₂O₂ +O=Fe(IV)-E -----> H₂O +Fe(III)-E

The catalytic process is thought to occur in two-stage

Fe-E represents iron center of heme attached to the rest of the enzyme (E)

when peroxide enters into active site which interacts with His⁷⁴ and Asn¹⁴⁷ where the first stage of reaction takes place.

via His74, transfer of a proton from one oxygen to peroxide which elongates and polarizes the O-O bond which breaks peroxide oxygen which is coordinated with the iron center.

Formation of Fe(IV)=O plus a heme radical occur during coordination.

the radical quickly degrades in another one-electron transfer to get rid of radical electron and leaving the heme ring unaltered.

During 2nd reaction, in a similar two-electron transfer reaction, Fe(IV)=O reacts with second hydrogen peroxide to produce the original Fe(III)-E and another water and oxygen molecule.

the prosthetic group is ferric protoporphyrin IX