Peroxisome
A peroxisome (IPA:
Peroxisomes are involved in the
.History
Peroxisomes (microbodies) were first described by a Swedish doctoral student, J. Rhodin in 1954.[8] They were identified as organelles by the Belgian cytologist Christian de Duve in 1967.[9] De Duve and co-workers discovered that peroxisomes contain several oxidases involved in the production of hydrogen peroxide (H2O2) as well as catalase involved in the decomposition of H2O2 to oxygen and water. Due to their role in peroxide metabolism, De Duve named them “peroxisomes”, replacing the formerly used morphological term “microbodies”. Later, it was described that firefly luciferase is targeted to peroxisomes in mammalian cells, allowing the discovery of the import targeting signal for peroxisomes, and triggering many advances in the peroxisome biogenesis field.[10][11]
Structure
Peroxisomes are small (0.1–1 µm diameter) subcellular compartments (organelles) with a fine, granular matrix and surrounded by a single biomembrane which are located in the cytoplasm of a cell.[12][13] Compartmentalization creates an optimized environment to promote various metabolic reactions within peroxisomes required to sustain cellular functions and viability of the organism.
The number, size and protein composition of peroxisomes are variable and depend on cell type and environmental conditions. For example, in baker's yeast (S. cerevisiae), it has been observed that, with good glucose supply, only a few, small peroxisomes are present. In contrast, when the yeasts were supplied with long-chain fatty acids as sole carbon source up to 20 to 25 large peroxisomes can be formed.[14]
Metabolic functions
A major function of the peroxisome is the breakdown of
The first reactions in the formation of
The specific metabolic pathways that occur exclusively in mammalian peroxisomes are:[5]
- α-oxidation of phytanic acid
- β-oxidation of very-long-chain and polyunsaturated fatty acids
- biosynthesis of plasmalogens
- conjugation of cholic acid as part of bile acid synthesis
Peroxisomes contain oxidative
Catalase, another peroxisomal enzyme, uses this H2O2 to oxidize other substrates, including phenols, formic acid, formaldehyde, and alcohol, by means of the peroxidation reaction:
- , thus eliminating the poisonous hydrogen peroxide in the process.
This reaction is important in liver and kidney cells, where the peroxisomes detoxify various toxic substances that enter the blood. About 25% of the ethanol that humans consume by drinking alcoholic beverages is oxidized to acetaldehyde in this way.[15] In addition, when excess H2O2 accumulates in the cell, catalase converts it to H2O through this reaction:
In higher plants, peroxisomes contain also a complex battery of antioxidative enzymes such as
There is evidence now that those reactive oxygen species including peroxisomal H2O2 are also important signalling molecules in plants and animals and contribute to healthy ageing and age-related disorders in humans.[20]
The peroxisome of plant cells is polarised when fighting fungal penetration. Infection causes a glucosinolate molecule to play an antifungal role to be made and delivered to the outside of the cell through the action of the peroxisomal proteins (PEN2 and PEN3).[21]
Peroxisomes in mammals and humans also contribute to anti-viral defense.[22] and the combat of pathogens [23]
Peroxisome assembly
Peroxisomes are derived from the
The degradation of peroxisomes is called pexophagy.[30]
Peroxisome interaction and communication
The diverse functions of peroxisomes require dynamic interactions and cooperation with many organelles involved in cellular lipid metabolism such as the endoplasmic reticulum, mitochondria, lipid droplets, and lysosomes.[31]
Peroxisomes interact with mitochondria in several metabolic pathways, including β-oxidation of fatty acids and the metabolism of reactive oxygen species.[5] Both organelles are in close contact with the endoplasmic reticulum and share several proteins, including organelle fission factors.[32] Peroxisomes also interact with the endoplasmic reticulum and cooperate in the synthesis of ether lipids (plasmalogens), which are important for nerve cells (see above). In filamentous fungi, peroxisomes move on microtubules by 'hitchhiking,' a process involving contact with rapidly moving early endosomes.[33] Physical contact between organelles is often mediated by membrane contact sites, where membranes of two organelles are physically tethered to enable rapid transfer of small molecules, enable organelle communication and are crucial for coordination of cellular functions and hence human health.[34] Alterations of membrane contacts have been observed in various diseases.
Associated medical conditions
Genes
PEX genes encode the protein machinery (peroxins) required for proper peroxisome assembly. Peroxisomal membrane proteins are imported through at least two routes, one of which depends on interaction between peroxin 19 and peroxin 3, while the other is required for import of peroxin 3, either of which may occur without the import of matrix (lumen) enzymes, which possess the peroxisomal targeting signal PTS1 or PTS2 as previously discussed.[37] Elongation of the peroxisome membrane and the final fission of the organelle are regulated by Pex11p.[38]
Genes that encode peroxin proteins include:
Evolutionary origins
The protein content of peroxisomes varies across species or organism, but the presence of proteins common to many species has been used to suggest an
Two independent evolutionary analyses of the peroxisomal
Other organelles of the
of filamentous fungi.See also
References
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Further reading
- Innovative Training Network PERICO
- Schrader M, Costello J, Godinho LF, Islinger M (2015). "Peroxisome-mitochondria interplay and disease". J Inherit Metab Dis. 38 (4): 681–702. S2CID 24392713.
- Schrader M, Fahimi HD (2008). "The peroxisome: still a mysterious organelle". Histochem Cell Biol. 129 (4): 421–440. PMID 18274771.
- Effelsberg D, Cruz-Zaragoza LD, Schliebs W, Erdmann R (2016). "Pex9p is a novel yeast peroxisomal import receptor for PTS1-proteins". Journal of Cell Science. 129 (21): 4057–4066. PMID 27678487.
- Yifrach E, Chuartzman SG, Dahan N, Maskit S, Zada L, Weill U, Yofe I, Olender T, Schuldiner M, Zalckvar E (2016). "Characterization of proteome dynamics in oleate reveals a novel peroxisome targeting receptor". Journal of Cell Science. 129 (21): 4067–4075. PMID 27663510.
- Mateos RM, León AM, Sandalio LM, Gómez M, del Río LA, Palma JM (December 2003). "Peroxisomes from pepper fruits (Capsicum annuum L.): purification, characterisation and antioxidant activity". Journal of Plant Physiology. 160 (12): 1507–16. PMID 14717445.
- Corpas FJ, Barroso JB (2014). "Functional implications of peroxisomal nitric oxide (NO) in plants". Frontiers in Plant Science. 5: 97. PMID 24672535.
- Corpas FJ (November 2015). "What is the role of hydrogen peroxide in plant peroxisomes?". Plant Biology. 17 (6): 1099–103. PMID 26242708.
- This article incorporates NCBI. Archived from the originalon 2009-12-08.