15.19: Peroxisomes
Peroxisomes are specialized organelles present in fungi, plant, and animal cells. It can vary in number, size, morphology, and activity depending on the type of tissue and the nutritional state of the cell. For example, cells with active lipid metabolism, such as adipocytes, neurons, and hepatocytes, have more peroxisomes than other cells in the body. Besides their primary role in breaking down complex organic molecules, peroxisomes can also synthesize specific macromolecules and participate in redox signaling.
Hydrogen peroxide: recycle and reuse
Peroxisomes act as a source as well as a sink for hydrogen peroxide. Oxidation of fatty acids releases hydrogen peroxide, which can either be degraded by catalase or oxidize another organic molecule such as ethanol. Furthermore, through specialized channel proteins present on their membrane, peroxisomes release hydrogen peroxide at low levels for participation in intracellular signaling pathways.
Peroxisomes in biosynthesis
Peroxisomes in the brain and heart cells synthesize plasmalogens, a class of glycerophospholipids present in myelin sheaths.
Peroxisomes in plant cells
In addition to β-oxidation of fatty acids, peroxisomes perform many diverse functions in plants. In leaves, they are involved in photorespiration and link chloroplast and mitochondria to recover any carbon lost during photosynthesis. Germinating seedlings contain specialized peroxisomes called glyoxysomes that convert lipids to sugars using the glyoxylate cycle and generate energy for the growing plant.
