Biology:Ascorbate peroxidase

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Short description: Enzyme
L-ascorbate peroxidase
APX-ascorbate.png
Structure of ascorbate peroxidase in complex with ascorbate (in blue); a histidine ligand (in red) coordinates to the iron of the heme group (also in red). Image taken from PDB 1OAF and created using Pymol
Identifiers
EC number1.11.1.11
CAS number72906-87-7
Databases
IntEnzIntEnz view
BRENDABRENDA entry
ExPASyNiceZyme view
KEGGKEGG entry
MetaCycmetabolic pathway
PRIAMprofile
PDB structuresRCSB PDB PDBe PDBsum
Gene OntologyAmiGO / 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 [math]\displaystyle{ \rightleftharpoons }[/math] dehydroascorbate + 2 H2O

It is a member of the family of heme-containing peroxidases. Heme peroxidases catalyse the H2O2-dependent oxidation of a wide range of different, usually organic, substrates in biology.

This enzyme belongs to the family of oxidoreductases, specifically those acting on a peroxide as acceptor (peroxidases). The systematic name of this enzyme class is L-ascorbate:hydrogen-peroxide oxidoreductase. Other names in common use include L-ascorbic acid peroxidase, L-ascorbic acid-specific peroxidase, ascorbate peroxidase, and ascorbic acid peroxidase. This enzyme participates in ascorbate and aldarate metabolism.

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.[5] APXs catalyse the H2O2-dependent oxidation of ascorbate in plants, algae and certain cyanobacteria.[6] APX has high sequence identity to cytochrome c peroxidase, which is also a class I peroxidase enzyme. Under physiological conditions, the immediate product of the reaction, the monodehydroascorbate radical, is reduced back to ascorbate by a monodehydroascorbate reductase (monodehydroascorbate reductase (NADH)) enzyme. In the absence of a reductase, two monodehydroascorbate radicals disproportionate rapidly to dehydroascorbic acid and ascorbate. APX is an integral component of the glutathione-ascorbate cycle.[7]

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 structures have been solved for this class of enzymes, with PDB accession codes 1APX, 1IYN, 1OAF, 1OAG, 1V0H, 2CL4, 2GGN, 2GHC, 2GHD, 2GHE, 2GHH, and 2GHK.

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

  1. ↑ "Soluble ascorbate peroxidase: detection in plants and use in vitamim C estimation". Die Naturwissenschaften 66 (12): 617–9. December 1979. doi:10.1007/bf00405128. PMID 537642. 
  2. ↑ "H2O2 destruction by ascorbate-dependent systems from chloroplasts". Biochimica et Biophysica Acta (BBA) - Bioenergetics 546 (3): 426–35. June 1979. doi:10.1016/0005-2728(79)90078-1. PMID 454577. 
  3. ↑ "Note sur la sophistication de la résine de jalap et sur les moyens de la reconnaître.". Bull Pharm. 2: 578–80. 1810. 
  4. ↑ "Cytochrome c Peroxidase.". Journal of Biological Chemistry 136 (3): 777–794. 1940. doi:10.1016/S0021-9258(18)73036-6. http://www.jbc.org/content/136/3/777.full.pdf. 
  5. ↑ "Superfamily of plant, fungal and bacterial peroxidases". Curr. Opin. Chem. Biol. 2 (3): 388–393. 1992. doi:10.1016/0959-440x(92)90230-5. 
  6. ↑ "Understanding functional diversity and substrate specificity in haem peroxidases: what can we learn from ascorbate peroxidase?". Natural Product Reports 20 (4): 367–81. August 2003. doi:10.1039/B210426C. PMID 12964833. 
  7. ↑ "ASCORBATE AND GLUTATHIONE: Keeping Active Oxygen Under Control". Annual Review of Plant Physiology and Plant Molecular Biology 49: 249–279. June 1998. doi:10.1146/annurev.arplant.49.1.249. PMID 15012235. 
  8. ↑ "Ascorbate Peroxidase Neofunctionalization at the Origin of APX-R and APX-L: Evidence from Basal Archaeplastida". Antioxidants 10 (4): 597. April 2021. doi:10.3390/antiox10040597. PMID 33924520. 
  9. ↑ "Identification of a porphyrin pi cation radical in ascorbate peroxidase compound I". Biochemistry 34 (13): 4342–5. April 1995. doi:10.1021/bi00013a024. PMID 7703248. 
  10. ↑ "Class I heme peroxidases: characterization of soybean ascorbate peroxidase". Archives of Biochemistry and Biophysics 360 (2): 173–8. December 1998. doi:10.1006/abbi.1998.0941. PMID 9851828. 
  11. ↑ "Crystal structure of recombinant pea cytosolic ascorbate peroxidase". Biochemistry 34 (13): 4331–41. April 1995. doi:10.1021/bi00013a023. PMID 7703247. 
  12. ↑ "Crystal structure of the ascorbate peroxidase-ascorbate complex". Nature Structural Biology 10 (4): 303–7. April 2003. doi:10.1038/nsb913. PMID 12640445. 
  13. ↑ "Interaction of ascorbate peroxidase with substrates: a mechanistic and structural analysis". Biochemistry 45 (25): 7808–17. June 2006. doi:10.1021/bi0606849. PMID 16784232. 
  14. ↑ "An analysis of substrate binding interactions in the heme peroxidase enzymes: a structural perspective". Archives of Biochemistry and Biophysics 500 (1): 13–20. August 2010. doi:10.1016/j.abb.2010.02.015. PMID 20206594. 
  15. ↑ "Engineered ascorbate peroxidase as a genetically encoded reporter for electron microscopy". Nature Biotechnology 30 (11): 1143–8. November 2012. doi:10.1038/nbt.2375. PMID 23086203. 
  16. ↑ "Directed evolution of APEX2 for electron microscopy and proximity labeling". Nature Methods 12 (1): 51–4. January 2015. doi:10.1038/nmeth.3179. PMID 25419960. 

Further reading

External links



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