Ascorbate peroxidase
| L-ascorbate peroxidase | |||||||||
|---|---|---|---|---|---|---|---|---|---|
ExPASy NiceZyme view | | ||||||||
| KEGG | KEGG entry | ||||||||
| MetaCyc | metabolic pathway | ||||||||
| PRIAM | profile | ||||||||
| PDB structures | RCSB PDB PDBe PDBsum | ||||||||
| Gene Ontology | AmiGO / QuickGO | ||||||||
| |||||||||
Ascorbate peroxidase (or L-ascorbate peroxidase, APX or APEX) (EC 1.11.1.11) is an enzyme that catalyzes the chemical reaction
- L-ascorbate + H2O2 dehydroascorbate + 2 H2O
It is a member of the family of
This enzyme belongs to the family of
Overview
Ascorbate-dependent peroxidase activity was first reported in 1979,[1],[2] more than 150 years after the first observation of peroxidase activity in horseradish plants[3] and almost 40 years after the discovery of the closely related cytochrome c peroxidase enzyme.[4]
Peroxidases have been classified into three types (class I, class II and class III): ascorbate peroxidases is a class I peroxidase enzyme.
Substrate specificity
APX enzymes show high specificity for ascorbate as an electron donor, but most APXs will also oxidise other organic substrates that are more characteristic of the class III peroxidases (such as horseradish peroxidase), in some cases at rates comparable to that of ascorbate itself. This means that defining an enzyme as an APX is not straightforward, but is usually applied when the specific activity for ascorbate is higher than that for other substrates. Some proteins from the APX family lack the ascorbate-binding amino acid residues suggesting that they might oxidize other molecules than ascorbate.[8]
Mechanism
Most of the information on mechanism comes from work on the pea cytosolic and soybean cytosolic enzymes. The mechanism of oxidation of ascorbate is achieved by means of an oxidized Compound I intermediate, which is subsequently reduced by substrate in two, sequential single electron transfer steps (equations [1]–[3], where HS = substrate and S• = one electron oxidised form of substrate).
- APX + H2O2 → Compound I + H2O [1]
- Compound I + HS → Compound II + S• [2]
- Compound II + HS → APX + S• + H2O [3]
In ascorbate peroxidase, Compound I is a transient (green) species and contains a high-valent iron species (known as ferryl heme, FeIV) and a porphyrin pi-cation radical,[9],[10] as found in horseradish peroxidase. Compound II contains only the ferryl heme.
Structural information
The structure of pea cytosolic APX was reported in 1995.[11] The binding interaction of soybean cytosolic APX with its physiological substrate, ascorbate[12],[13] and with a number of other substrates[14] are also known.
As of late 2007, 12
Applications in cellular imaging
Both pea APX[15] and soybean APX and their mutants (APEX, APEX2)[16] have been used in electron microscopy studies for cellular imaging.
See also
References
- S2CID 12729653.
- PMID 454577.
- ^ Planche LA (1810). "Note sur la sophistication de la résine de jalap et sur les moyens de la reconnaître". Bull Pharm. 2: 578–80.
- .
- .
- PMID 12964833.
- PMID 15012235.
- PMID 33924520.
- PMID 7703248.
- PMID 9851828.
- PMID 7703247.
- S2CID 32035409.
- PMID 16784232.
- PMID 20206594.
- PMID 23086203.
- PMID 25419960.
Further reading
- Shigeoka S, Nakano Y, Kitaoka S (April 1980). "Purification and some properties of L-ascorbic-acid-specific peroxidase in Euglena gracilis Z". Archives of Biochemistry and Biophysics. 201 (1): 121–7. PMID 6772104.
- Shigeoka S, Nakano Y, Kitaoka S (January 1980). "Metabolism of hydrogen peroxide in Euglena gracilis Z by L-ascorbic acid peroxidase". The Biochemical Journal. 186 (1): 377–80. PMID 6768357.
- Shigeoka, Shigeru; Ishikawa, Takahiro; Tamoi, Masahiro; Miyagawa, Yoshiko; Takeda, Toru; Yabuta, Yukinori; Yoshimura, Kazuya (15 May 2002). "Regulation and function of ascorbate peroxidase isoenzymes". Journal of Experimental Botany. 53 (372): 1305–1319. PMID 11997377.
External links
- EC 1.11.1.11 Archived 2011-05-16 at the Wayback Machine
- L-ascorbate peroxidase (EC-Number 1.11.1.11 ) Archived 2012-02-04 at the Wayback Machine
