peroxisomal

Peroxisomal refers to anything related to peroxisomes, small, single-membrane-bound organelles present in nearly all eukaryotic cells. Peroxisomes house enzymes that carry out diverse metabolic functions, including beta-oxidation of very long-chain fatty acids, detoxification of reactive oxygen species, and various steps in lipid and bile acid metabolism. In plants, peroxisomes also participate in photorespiration and fatty acid breakdown, while in animals they contribute to plasmalogen synthesis and hydrogen peroxide metabolism.

Structure and biogenesis: Peroxisomes contain a dense matrix of enzymes enclosed by a single lipid bilayer. They multiply by growth and division and can form de novo from the endoplasmic reticulum. Import of most matrix proteins relies on peroxisomal targeting signals: PTS1, a C-terminal tripeptide (often Ser-Lys-Leu), and PTS2, an N-terminal signal. Receptors Pex5 (PTS1) and Pex7 (PTS2) ferry cargo to the importing machinery, which includes membrane proteins such as Pex13 and Pex14. Import can accommodate folded proteins and even protein complexes, after which enzymes are activated in the matrix.

Functions and clinical relevance: Peroxisomes oxidize very long-chain and branched-chain fatty acids via specific oxidases, producing hydrogen peroxide that is subsequently detoxified by catalase. They contribute to plasmalogen lipid synthesis, important for membrane structure, and participate in bile acid formation. Disruptions in peroxisome biogenesis or function cause human disorders, collectively termed peroxisomal biogenesis disorders, including Zellweger spectrum disorders. X-linked adrenoleukodystrophy, due to ABCD1 transporter defects, leads to accumulation of very long-chain fatty acids. Peroxisomal function is essential for normal development and lipid homeostasis.