Paraoxonase
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Paraoxonases are a family of mammalian enzymes with aryldialkylphosphatase activity. There are three paraoxonase isozymes, which were originally discovered for their involvement in the hydrolysis of organophosphates.[1]
Research has indicated the enzymatic activity of paraoxonases is more diversified than its activity as an organophosphatase. Esterase and lactonase activity has also been observed from these enzymes and though the physiologically relevant substrates for these enzymes are unknown, it is likely that lactones are the main substrate (although there is a relatively high level of variation in substrate specificity among these enzymes). Most of the studies on the paraoxonase family have specifically looked at the paraoxonase 1 type, leaving much to be learned about the remaining two.[2]
The study of this enzyme family has many potential consequences in preventative medicine and toxicology as well as in certain societal contexts. The genes that encode for these enzymes have a number of different
Types
There are three known paraoxonases, which are encoded by the genes PON1, PON2 and PON3, located on the long arm of chromosome 7 in humans.[1][6] The differences between them lie in their locations and activities.
- Paraoxonase 1 has gene expression primarily in the liver but has also been expressed in tissue from the kidney and parts of the colon.[7] Paraoxonase 1 that is synthesized in the liver is then transported into the bloodstream, where it will associate with high-density lipoprotein (HDL). It has been shown to have broad substrate specificity and has proved to protect against exposure to some organophosphates (such as those from insecticides) by hydrolyzing potentially toxic metabolites.[8][9] Paraoxonase 1 also plays an important role as an antioxidant in preventing the oxidation of low-density lipoproteins (LDL), a process that is directly involved in the development of atherosclerosis. Its serum concentration is influenced by inflammatory changes and the levels of serum oxidised-LDL.
- Paraoxonase 2 is a ubiquitously expressed intracellular protein that can protect cells against oxidative damage.[10] While paraoxonase 2 shares similar antioxidant properties with its two enzyme counterparts, it lacks the ability to hydrolyze some of the organophosphate metabolites.
- Paraoxonase 3 is similar to type 1 in activity but differs from it in substrate specificity. Serum PON3 activity is one hundredth that of PON1. Additionally, it is not regulated by inflammation and levels of oxidised lipids.[11] Both paraoxonase 1 and 3 are bound to HDL and because of their similar properties as antioxidants, it is possible PON3 also plays a role in the prevention of LDL and HDL oxidation.[12]
Biological function
Paraoxonases have been found to perform a number of biological functions, though the primary role of this group of enzymes is still a topic of speculation. Some of the observed roles have revealed activities of anti-
Mechanism
The study of this family of enzymes has been something of interest for a number of years now;[
Regulation
One of the common inhibitors of enzymatic activity (for PON 1 and PON 3) is lipid
Clinical significance
The development of
History
PON was identified as an enzyme having organophosphates as its
The 3D crystal structure of PON1 was determined in 2004.[19]
References
- ^ PMID 15459089.
- ^ Litvinov, Dmitry, Halleh Mahini, and Mahdi Garelnabi. “Antioxidant and Anti-Inflammatory Role of Paraoxonase 1: Implication in Arteriosclerosis Diseases.” North American Journal of Medical Sciences 4.11 (2012): 523–532. PMC. Web. 1 Mar. 2016.
- ^ a b Costa, Lucio G., and Clement E. Furlong. Paraoxonase (PON1) in Health and Disease: Basic and Clinical Aspects. Boston: Kluwer Academic, 2002. Print.
- ^ a b S.D. Nguyen, D.E. Sok. “Oxidative inactivation of Paraoxonase 1 an antioxidant protein and its effect on antioxidant action.” Free Radic Res, 37 (2003), pp. 77–83
- ^ Egon A. Ozer, Alejandro Pezzulo, Diana M. Shih, Carlene Chun, Clement Furlong, Aldons J. Lusis, Everett P. Greenberg, Joseph Zabner. Human and murine paraoxonase 1 are host modulators of Pseudomonas aeruginosa quorum-sensing FEMS Microbiology Letters Dec 2005, 253 (1) 29-32; DOI: 10.1016/j.femsle.2005.09.023
- S2CID 1814007.
- ^ Mackness, B., Beltran-Debon, R., Aragones, G., Joven, J., Camps, J. and Mackness, M. (2010), Human tissue distribution of paraoxonases 1 and 2 mRNA. IUBMB Life, 62: 480–482. doi: 10.1002/iub.347
- ^ Richter, Rebecca J. et al. “Paraoxonase 1 Status as a Risk Factor for Disease or Exposure.” Advances in Experimental Medicine and Biology 660 (2010): 29–35. PMC. Web. 1 Mar. 2016.
- ^ a b Tomas, Marta, Gloria Latorre, Mariano Senti, and Jaume Marrugat. "The Antioxidant Function of High Density Lipoproteins: A New Paradigm in Atherosclerosis." Revista Española De Cardiologia 57.06 (2004): n. pag. Web. 22 Feb. 2016.
- PMID 11579088.
- PMID 11304470.
- ^ Draganov DI, Teiber JF, Speelman A, et al. Human paraoxonases (PON1, PON2, and PON3) are lactonases with overlapping and distinct substrate specificities. J Lipid Res 2005;46:1239-42
- ^ a b Aggarwal G, Prajapati R, Tripathy RK, Bajaj P, Iyengar ARS, Sangamwar AT, et al. (2016) Toward Understanding the Catalytic Mechanism of Human Paraoxonase 1: Site-Specific Mutagenesis at Position 192. PLoS ONE 11(2): e0147999. doi:10.1371/journal.pone.0147999
- ^ Mackness M. I., Durrington P. N., Mackness B. The role of paraoxonase 1 activity in cardiovascular disease: potential for therapeutic intervention. American Journal of Cardiovascular Drugs. 2004;4(4):211–217. doi: 10.2165/00129784-200404040-00002
- ^ a b Le, Quang Anh Tuan, et al. "Insights into the Lactonase Mechanism of Serum Paraoxonase 1 (PON1): Experimental and Quantum Mechanics/Molecular Mechanics (QM/MM) Studies." The Journal of Physical Chemistry B 119.30 (2015):9571-9585. Web.
- ^ Manzo, Luigi. "Organophosphates." Occupational Neurotoxicology. By Lucio G. Costa. N.p.: CRC LLC, 1998. 87-89. Print.
- ^ Ruiz J, Blanche H, James RW, Garin MC, Vaisse C, Charpentier G, et al. Gln-Arg192 polymorphism of paraoxonase and coronary heart disease in type 2 diabetes. Lancet. 1995;346:869–72.
- PMID 20013192.
- S2CID 52874893.)
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