peroxisomesorganelles

Peroxisomes are small, single-membrane-bound organelles found in the cytoplasm of most eukaryotic cells. They vary in number and size by tissue and metabolic state and contain a collection of oxidative enzymes within their matrix.

The peroxisomal matrix harbors enzymes involved in lipid metabolism and detoxification. A central enzyme is catalase, which converts hydrogen peroxide into water and oxygen, reducing reactive oxygen species. Peroxisomes also carry out beta-oxidation of very-long-chain and certain branched-chain fatty acids and participate in the synthesis of ether phospholipids such as plasmalogens, important components of cellular membranes. In the liver, they contribute to bile acid synthesis and other metabolic pathways. In plants and some microorganisms, peroxisomes are involved in photorespiration and the glyoxylate cycle.

Biogenesis and protein import are tightly regulated. Peroxisomal proteins are imported post-translationally via targeting signals, notably PTS1 and PTS2, recognized by cytosolic receptors and delivered to the peroxisome. The import machinery includes several peroxins (Pex proteins) that help dock, translocate, and assemble matrix enzymes. Peroxisomes can grow by importing lipids and proteins and then divide; new peroxisomes can also form de novo from the endoplasmic reticulum.

Clinical relevance: Peroxisomal disorders arise from defects in biogenesis or in specific peroxisomal enzymes, leading to accumulation of fatty acids and metabolic dysfunction. Examples include Zellweger spectrum disorders and X-linked adrenoleukodystrophy, which can affect neurological and hepatic function.

Overall, peroxisomes are essential for lipid processing and cellular detoxification, contributing to cellular homeostasis and metabolism.