Peroxisomes

Peroxisomes are essential subcellular organelles in eukaryotic cells, which serve the degradation of various cellular metabolites (e.g. fatty acids) and the synthesis of e.g. glycerophospholipids (Wanders RJ 2014).

Peroxisomes appear as 0.2 to 1.0 µm large, round organelles surrounded by a single-layer lipid membrane. They are detected in increased density in hepatocytes.

Numerous (up to 50) mono- and dioxygenases that fuse free radicals can be detected in the peroxisomes. These are thus restricted in their reactivity. The best known and name-giving enzymes of the peroxisomes are the peroxidases, including catalase, which inactivates hydrogen peroxide by converting it into oxygen and water (De Munter S et al. 2015).

Besides binding free radicals, peroxisomes are able to oxidize fatty acids to acetyl-CoA. The resulting activated acetic acid can be transported into the cytosol by a transporter. Here it is available for the formation of fatty acids and cholesterol.

Mutations of the genes coding for peroxisomes, such as the PEX-1, PEX-5 genes, lead to a defective function of the peroxisomes (Braverman NE et al. 2012). The consequences are multisystem diseases such as Zellweger syndrome and congenital adrenoleukodystrophy. In these cases, saturated very-long-chain fatty acids (VLCFA such as phytic acid, cerotic acid, brassy acid) are deposited in the cells of organs with particularly high metabolic activity or excreted as pathological excretion products in the urine (they are detectable in the urine) Wanders RJ (2014).

1. Braverman NE et al (2012) Functions of plasmalogen lipids in health and disease.Biochim Biophys Acta 1822:1442-2452.
2. De Munter S et al (2015) Peroxisomal Disorders: A Review onCerebellar Pathologies. Brain Pathol 25:663-678.
3. Wanders RJ (2014) Metabolic functions of peroxisomes in health and disease. Biochemistry 98:36-44.