Peroxisomes

Unlike mitochondria, peroxisomes do not contain DNA or ribosomes. Thus all of their proteins must be imported from the cytosol. As with mitochondria and the ER, new perosisomes arise from fission from preexisting peroxisomes.

Peroxisomes catalyze the first reactions in the formation of plasmalogens which are the most abundant class of phosphlipids in myelin. Deficiency of plasmalogens causes profound abnormalities in the myleination of nerve cells. In addition to an ethanolamine head group, plasmalogens contain a glycerol phosphate backbone which is attached to a fatty acid which contains an ether linkage.

Peroxisomes also contain enzyme(s) that use molecular oxygen to remove hydrogen atoms in an oxidative reaction that produces hydrogen peroxide (H₂O₂) which is then used in the liver and kidney cells to oxidize other substrates to detoxify other molecules.

A specific sequence, SKL (serine, lysine, leucine) at the C terminus of many peroxisomal proteins serves as an import signal to peroxisomes. There are soluble receptor proteins called peroxins. A peroxin pex receptor for example accompanies its cargo all the way into peroxisomes much like protein transport into the nucleus. Thus the protein folds as it is transported just as with nuclear transport and ATP is required.

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