Peroxisomes are small cellular organelles involved in various metabolic processes, including the degradation of metabolites and the synthesis of plasmalogens.
Extract
[...] The peroxisomal matrix contains numerous enzymes involved in oxidation reactions. Peroxisomes lack a genome, ribosomes, translation machinery, do not produce ATP, and are not surrounded by a double membrane. Their origin is not considered strictly endosymbiotic like that of mitochondria, but they could represent an ancient cellular adaptation intended to protect the cell against the toxicity of oxygen. In fact, peroxisomal oxidases use oxygen to catalyze their reactions, generating hydrogen peroxide which allows the degradation of many metabolites and contributes to certain steps of cellular respiration. [...]
[...] The specific proteins of peroxisomes are called peroxins and are encoded by PEX genes. There are approximately 24 peroxins: peroxin 11 participates in the renewal and division of peroxisomes, while peroxins and 19 are involved in the formation of the peroxisomal membrane. The peroxisomal amino-oxidases are involved in the metabolism of certain amino acids. The peroxisomes also participate in the synthesis of plasmalogens, a particular type of phosphoglyceride containing ether and not ester bonds. Ethanolamine plasmalogens are predominant in the brain, while those containing choline are mainly found in the heart. [...]
[...] The proteins destined for the peroxisome carry targeting sequences called PTS (Peroxisomal Targeting Signals), specific to peroxisomes. There are two main types of signals: PTS1, located at the C-terminal end, and PTS2, located at the N-terminal end. Once mature, the peroxisome can integrate into the peroxisomal network via canaliculi, then undergo budding and fission phenomena to give rise to new peroxisomes, a process dependent on the peroxin 11. Peroxisomes are dynamic organelles that move along microtubules. Their lifespan is short and depends on the cell type (approximately 3 to 5 days in hepatocytes). [...]
[...] They play a crucial role in oxidative metabolism, particularly in the beta-oxidation of very long-chain fatty acids (VLCFAs). These fatty acids are first activated in the cytosol in the form of acyl-CoA, then taken over by peroxisomal beta-oxidation (Lynen pathway). This pathway produces acetyl-CoA, NADH, and FADH?. Unlike the mitochondria, FADH? is reoxidized in the peroxisome during redox reactions producing hydrogen peroxide, without direct energy production. Peroxisomes have an oval or spherical structure dependent on cellular activity, with a diameter ranging from 0.5 to 1 µm (500-1000 nm). [...]
[...] Peroxisomal proteins are synthesized by free cytosolic ribosomes. Proteins carrying a PTS1 signal are recognized by peroxin while those carrying a PTS2 signal are recognized by peroxin 7. After recognition, the protein-peroxin complexes are directed towards the peroxisomal membrane, then docked by peroxins and 17. A step involving dislocation and translocation then allows the import of the protein. Dissociation ensures the recycling of peroxins 5 and while translocation to the matrix occurs via a permease composed of peroxins and 12. Dismutation reaction: 2 ? [...]
