Peroxisome
Organelles that generate and break down hydrogen peroxide.
Peroxisomes are membrane-bound organelles, a type of microbody, found in the cytoplasm of virtually all eukaryotic cells. They are oxidative organelles that generate and scavenge hydrogen peroxide, performing key roles in lipid metabolism and the reduction of reactive oxygen species. Peroxisomes are involved in the catabolism of very long chain fatty acids, branched chain fatty acids, bile acid intermediates, D-amino acids, and polyamines, as well as the biosynthesis of plasmalogens, ether phospholipids critical for normal brain and lung function in mammals.
- field
- Cell biology
- known_for
- Hydrogen peroxide metabolism, lipid metabolism, and peroxisome biogenesis
- key_enzymes
- Catalase, D-amino acid oxidase, uric acid oxidase
Lore & Background
Peroxisomes were first described by Swedish doctoral student J. De Duve and co-workers discovered that peroxisomes contain several oxidases involved in the production of hydrogen peroxide as well as catalase involved in its decomposition. Due to their role in peroxide metabolism, De Duve named them 'peroxisomes,' replacing the former 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.
Reader's Guide
Peroxisomes are small (0.1–1 μm diameter) organelles with a fine, granular matrix, surrounded by a single biomembrane. Their number, size, and protein composition vary depending on cell type and environmental conditions. A major function is the breakdown of very long chain fatty acids through beta oxidation; in animal cells, these are converted to medium chain fatty acids and shuttled to mitochondria, while in yeast and plant cells the process occurs exclusively in peroxisomes. Peroxisomes also initiate plasmalogen formation, produce bile acids, and contain oxidative enzymes such as D-amino acid oxidase and uric acid oxidase (the latter absent in humans, explaining gout). They detoxify toxic substances, including about 25% of consumed ethanol, and in plants contain antioxidative enzymes. Peroxisomes generate reactive oxygen species that are important signaling molecules in plants and animals, contributing to healthy aging and age-related disorders. They also contribute to anti-viral defense and combat pathogens. Peroxisomes are derived from the smooth endoplasmic reticulum under certain conditions and replicate by membrane growth and division. Matrix proteins are imported via specific targeting signals (PTS1 or PTS2) without needing to be unfolded, using peroxins (36 known, 13 in mammals).
Did You Know?
- Peroxisomes contain approximately 10% of the total activity of two enzymes in the pentose phosphate pathway.
- In baker's yeast, only a few small peroxisomes are present with good glucose supply, but up to 20–25 large ones form when supplied with long-chain fatty acids.
- About 25% of ethanol consumed by humans is oxidized to acetaldehyde in peroxisomes.
- Uric acid oxidase is absent in humans, explaining the disease known as gout.
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