Ascorbate peroxidase explained

L-ascorbate peroxidase
Ec Number:1.11.1.11
Cas Number:72906-87-7
Go Code:0016688

Ascorbate peroxidase (or L-ascorbate peroxidase, APX or APEX) is an enzyme that catalyzes the chemical reaction

L-ascorbate + H2O2

\rightleftharpoons

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,,,,,,,,,,, and .

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

Further reading

External links

Notes and References

  1. Kelly GJ, Latzko E . Soluble ascorbate peroxidase: detection in plants and use in vitamim C estimation . Die Naturwissenschaften . 66 . 12 . 617–9 . December 1979 . 537642 . 10.1007/bf00405128 . 12729653 .
  2. Groden D, Beck E . H2O2 destruction by ascorbate-dependent systems from chloroplasts . Biochimica et Biophysica Acta (BBA) - Bioenergetics . 546 . 3 . 426–35 . June 1979 . 454577 . 10.1016/0005-2728(79)90078-1 .
  3. Planche LA . Note sur la sophistication de la résine de jalap et sur les moyens de la reconnaître. . Bull Pharm. . 1810 . 2 . 578–80 .
  4. Altschul AM, Abrams R, Hogness TR . Journal of Biological Chemistry . Cytochrome c Peroxidase. . 136 . 777–794 . 1940 . 3 . 10.1016/S0021-9258(18)73036-6 . free .
  5. Welinder KG . Superfamily of plant, fungal and bacterial peroxidases . Curr. Opin. Chem. Biol. . 2 . 3 . 388–393 . 1992 . 10.1016/0959-440x(92)90230-5.
  6. Raven EL . 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 . 12964833 . 10.1039/B210426C .
  7. Noctor G, Foyer CH . ASCORBATE AND GLUTATHIONE: Keeping Active Oxygen Under Control . Annual Review of Plant Physiology and Plant Molecular Biology . 49 . 249–279 . June 1998 . 15012235 . 10.1146/annurev.arplant.49.1.249 .
  8. Lazzarotto F, Menguer PK, Del-Bem LE, Zámocký M, Margis-Pinheiro M . Ascorbate Peroxidase Neofunctionalization at the Origin of APX-R and APX-L: Evidence from Basal Archaeplastida . Antioxidants . 10 . 4 . 597 . April 2021 . 33924520 . 8069737 . 10.3390/antiox10040597 . free .
  9. Patterson WR, Poulos TL, Goodin DB . Identification of a porphyrin pi cation radical in ascorbate peroxidase compound I . Biochemistry . 34 . 13 . 4342–5 . April 1995 . 7703248 . 10.1021/bi00013a024 .
  10. Jones DK, Dalton DA, Rosell FI, Raven EL . Class I heme peroxidases: characterization of soybean ascorbate peroxidase . Archives of Biochemistry and Biophysics . 360 . 2 . 173–8 . December 1998 . 9851828 . 10.1006/abbi.1998.0941 .
  11. Patterson WR, Poulos TL . Crystal structure of recombinant pea cytosolic ascorbate peroxidase . Biochemistry . 34 . 13 . 4331–41 . April 1995 . 7703247 . 10.1021/bi00013a023 .
  12. Sharp KH, Mewies M, Moody PC, Raven EL . Crystal structure of the ascorbate peroxidase-ascorbate complex . Nature Structural Biology . 10 . 4 . 303–7 . April 2003 . 12640445 . 10.1038/nsb913 . 32035409 .
  13. Macdonald IK, Badyal SK, Ghamsari L, Moody PC, Raven EL . Interaction of ascorbate peroxidase with substrates: a mechanistic and structural analysis . Biochemistry . 45 . 25 . 7808–17 . June 2006 . 16784232 . 10.1021/bi0606849 .
  14. Gumiero A, Murphy EJ, Metcalfe CL, Moody PC, Raven EL . 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 . 20206594 . 10.1016/j.abb.2010.02.015 .
  15. Martell JD, Deerinck TJ, Sancak Y, Poulos TL, Mootha VK, Sosinsky GE, Ellisman MH, Ting AY . 6 . Engineered ascorbate peroxidase as a genetically encoded reporter for electron microscopy . Nature Biotechnology . 30 . 11 . 1143–8 . November 2012 . 23086203 . 3699407 . 10.1038/nbt.2375 .
  16. Lam SS, Martell JD, Kamer KJ, Deerinck TJ, Ellisman MH, Mootha VK, Ting AY . Directed evolution of APEX2 for electron microscopy and proximity labeling . Nature Methods . 12 . 1 . 51–4 . January 2015 . 25419960 . 4296904 . 10.1038/nmeth.3179 .

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