#peroxisomes

Basics of Cell Biology

Which of the following organelles is involved in detoxification?

Detoxification of endogenous metabolites and exogenous xenobiotics requires oxidative handling and compartmentalization to protect cellular components. Peroxisomes, single membrane organelles containing enzymes imported via peroxisomal targeting signals PTS1 C-terminal SKL tripeptide and PTS2 N-terminal recognized by shuttling receptors PEX5 and PEX7, house acyl-CoA oxidases that beta-oxidize very-long-chain fatty acids C22 and above and branched-chain fatty acids like phytanic acid generating acetyl-CoA for mitochondria plus hydrogen peroxide H2O2 as byproduct. Catalase, core component with h

Ref: Alberts et al., Molecular Biology of the Cell, 7th ed., Chapter 12: Peroxisomes and Detoxification.

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Cell Organelles

Which of the following statements is false regarding peroxisomes?

Peroxisomes are single-membrane organelles morphologically and functionally distinct from lysosomes despite both participating in degradative metabolism. Transmission electron microscopy shows spherical vesicles 0.1 to 1 micrometer with electron-dense crystalline cores composed of urate oxidase in rat or dense catalase aggregates in humans. Unlike double-membrane mitochondria and nucleus, peroxisomes are bounded by single phospholipid bilayer enriched in peroxisomal membrane proteins PMP70, ALDP, PEX11 isoforms and containing import translocon. Their matrix contains oxidative enzymes such as a

Ref: Smith & Aitchison, Cold Spring Harbor Perspect Biol 2013: Peroxisomes Originate from ER and Contain Oxidases.

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Cell Organelles

Which enzyme in peroxisomes detoxifies H₂O₂?

Because peroxisomal oxidases produce stoichiometric hydrogen peroxide during oxidation of fatty acids, urate, D-amino acids and polyamines, cells require robust detoxification to prevent oxidative damage to proteins, lipids and DNA. Catalase is the signature antioxidant enzyme residing in peroxisomal matrix, often forming electron-dense crystalline core visible by electron microscopy in rat liver. It is a 240 kDa heme-containing homotetramer that disproportionates hydrogen peroxide into water and molecular oxygen with extremely high turnover number near ten million molecules per second, one of

Ref: Alberts et al., Molecular Biology of the Cell, 6th ed., Chapter 12: Peroxisomes and Catalase Function.

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Cell Organelles

What is the major function of peroxisomes?

Peroxisomes are ubiquitous single-membrane organelles present in most eukaryotes central to lipid metabolism, ROS balance, and signaling. Their hallmark metabolic function is beta-oxidation of very-long-chain fatty acids longer than 22 carbons, branched-chain fatty acids like phytanic acid requiring alpha-oxidation first, and polyunsaturated fatty acids that mitochondria cannot handle efficiently due to double bond positions. Unlike mitochondrial beta-oxidation coupled to electron transfer flavoprotein and respiratory chain to produce ATP, peroxisomal acyl-CoA oxidases, ACOX1, ACOX2, ACOX3, tr

Ref: Wanders & Waterham, Annual Review of Biochemistry 2016: Peroxisome Biogenesis and Fatty Acid Beta-Oxidation.

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Cell Organelles

The major function of peroxisomes is:

Peroxisomes are single membrane oxidative organelles discovered by Rhodin and De Duve, numbering hundreds per cell, containing more than fifty enzymes producing and degrading hydrogen peroxide. Beta-oxidation of very long chain fatty acids greater than twenty two carbons, branched phytanic acid alpha-oxidation, bile acid intermediate shortening and ether lipid synthesis of plasmalogens providing antioxidant membranes and myelin components occur via enzymes acyl-CoA oxidase generating H2O2, bifunctional enzyme and thiolase. Catalase converts two H2O2 to water and oxygen detoxifying, also urate

Ref: Wanders Annu Rev Biochem; peroxisome beta-oxidation VLCFA catalase PTS1 PTS2 Pex import.

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