Catalase

Three types of catalases. The first two (human and bacterial) use hemoglobin-bound iron to bind to oxygen, while the third (a pseudocatalase) uses manganese (metals shown in light blue). From Molecule of the Month (RCSB PDB) by David Goodsell based on PDB-IDs Thioester protein crosslinks, Thioether protein crosslinks, and 1jku.

Function

Catalase (CAT) catalyzes the conversion of hydrogen peroxide to water and oxygen. CAT contains porphyrin-heme Fe group which reacts with the hydrogen peroxide. CAT containing Mn are called pseudocatalase (PCAT). Catalase-peroxidase (CAT KatG) is a bifunctional enzyme with both catalase and peroxidase activities. CAT KatG cofactor is a heme group. It provides defense against oxidative stress by reducing hydrogen peroxide. Mutations in CAT KatG can cause resistance to the anti-malarial drug isoniazid (INH). Catalase-phenol oxidase (CATPO) is a heme-containing CAT which shows phenol oxidase activity.

There are four oxygen atoms total in the reactants. Which do you think will be paired up after the reaction is completed (i.e. in the dixoxygen molecule O₂ from as one of the products)?

Structure

spinqualitylabelsall models E. coli catalase Hpii tetramer showing the heme groups in yellow. PDB-ID 1gge Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image   Print3D Catalase is a tetramer, each polypeptide chain is over 500 amino acids long. It contains four porphyrin heme (iron) groups that allow the enzyme to react with the hydrogen peroxide. Coordination of iron in E. coli catalase is by the four nitrogen atoms of the heme molecule, an oxygen from a tyrosine side chain and a water molecule (water molecules are shown as red spheres). As hydrogen peroxide enters the active site, it interacts with the amino acids Asn147 (asparagine at position 147) and His74, causing a proton (hydrogen ion) to transfer between the oxygen atoms. The free oxygen atom coordinates, freeing the newly formed water molecule and Fe(IV)=O. Fe(IV)=O reacts with a second hydrogen peroxide molecule to reform Fe(III)-E and produce water and oxygen. The reactivity of the iron center may be improved by the presence of the phenolate ligand of Tyr357 in the fifth iron ligand, which can assist in the oxidation of the Fe(III) to Fe(IV). The efficiency of the reaction may also be improved by the interactions of His74 and Asn147 with reaction intermediates. See also: Thioester protein crosslinks and Thioether protein crosslinks.

pH dependence

The following video shows how the rate of the potato catalase depends on the pH. Do you have a hypothesis why both low and high pH slow down the enzyme compared to neutral pH? Which acid/base groups are part of the mechanism described above? How is the structure (shape) of the enzyme affected by changes in pH?

See also

Ann Taylor/Catalase
Human Erythrocyte Catalase
Catalase 2CAG bcce2014.
See also Catalase (Hebrew).

3D Structures of catalase

Catalase 3D structures

Proteopedia Page Contributors and Editors (what is this?)

Karsten Theis, Michal Harel, Ann Taylor, Alexander Berchansky