Catalase: Difference between revisions
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[[Image:Catalases MotM57.png| 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. From [https://pdb101.rcsb.org/motm/57 Molecule of the Month] (RCSB PDB) by David Goodsell | [[Image:Catalases MotM57.png| 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 [https://pdb101.rcsb.org/motm/57 Molecule of the Month] (RCSB PDB) by David Goodsell based on PDB-IDs [[1qqw]], [[1iph]], and [[1jku]].|thumb|500px|right]] | ||
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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 O<sub>2</sub> from as one of the products)? | 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 O<sub>2</sub> from as one of the products)? | ||
== Structure == | == Structure == | ||
<StructureSection load='1gge' size='350' side='right' scene='46/467276/Cv/1' caption='E. coli catalase Hpii tetramer showing the heme groups in yellow. PDB-ID [[1gge]]'> | |||
Catalase is a <scene name='46/467276/Cv/2'>tetramer</scene>, each polypeptide chain is over 500 amino acids long. It contains <scene name='46/467276/Cv/3'>four porphyrin heme (iron) groups</scene> that allow the enzyme to react with the hydrogen peroxide. <scene name='46/467276/Cv/7'>Coordination of | Catalase is a <scene name='46/467276/Cv/2'>tetramer</scene>, each polypeptide chain is over 500 amino acids long. It contains <scene name='46/467276/Cv/3'>four porphyrin heme (iron) groups</scene> that allow the enzyme to react with the hydrogen peroxide. <scene name='46/467276/Cv/7'>Coordination of iron</scene> 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).<ref>PMID:11455600</ref> | ||
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.<ref>PMID:11455600</ref> | 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.<ref>PMID:11455600</ref> | ||
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==pH dependence== | ==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? | 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? | ||
<html5media height="300" width="360">https://www.youtube.com/watch?v=58CuZHUe91E</html5media> | <html5media height="300" width="360">https://www.youtube.com/watch?v=58CuZHUe91E</html5media> | ||