Peroxisome
Peroxisomes also play a role in the biosynthesis of plasmalogens: ether phospholipids critical for the normal function of mammalian brains and lungs.
[5] Other peroxisomal functions include the glyoxylate cycle in germinating seeds ("glyoxysomes"), photorespiration in leaves,[7] glycolysis in trypanosomes ("glycosomes"), and methanol and amine oxidation and assimilation in some yeasts.
[10] Due to their role in peroxide metabolism, De Duve named them “peroxisomes”, replacing the formerly used morphological term “microbodies”.
[11][12] Peroxisomes are small (0.1–1 μm diameter) subcellular compartments (organelles) with a fine, granular matrix and surrounded by a single biomembrane which are located in the cytoplasm of a cell.
[13][14] Compartmentalization creates an optimized environment to promote various metabolic reactions within peroxisomes required to sustain cellular functions and viability of the organism.
For example, in baker's yeast (S. cerevisiae), it has been observed that, with good glucose supply, only a few, small peroxisomes are present.
In contrast, when the yeasts were supplied with long-chain fatty acids as sole carbon source up to 20 to 25 large peroxisomes can be formed.
Deficiency of plasmalogens causes profound abnormalities in the myelination of nerve cells, which is one reason why many peroxisomal disorders affect the nervous system.
Certain enzymes within the peroxisome, by using molecular oxygen, remove hydrogen atoms from specific organic substrates (labeled as R), in an oxidative reaction, producing hydrogen peroxide (H2O2, itself toxic): Catalase, another peroxisomal enzyme, uses this H2O2 to oxidize other substrates, including phenols, formic acid, formaldehyde, and alcohol, by means of the peroxidation reaction: This reaction is important in liver and kidney cells, where the peroxisomes detoxify various toxic substances that enter the blood.
[16] In addition, when excess H2O2 accumulates in the cell, catalase converts it to H2O through this reaction: In higher plants, peroxisomes contain also a complex battery of antioxidative enzymes such as superoxide dismutase, the components of the ascorbate-glutathione cycle, and the NADP-dehydrogenases of the pentose-phosphate pathway.
[19][20] There is evidence now that those reactive oxygen species including peroxisomal H2O2 are also important signalling molecules in plants and animals and contribute to healthy ageing and age-related disorders in humans.
Infection causes a glucosinolate molecule to play an antifungal role to be made and delivered to the outside of the cell through the action of the peroxisomal proteins (PEN2 and PEN3).
[23] and the combat of pathogens [24] Peroxisomes are derived from the smooth endoplasmic reticulum under certain experimental conditions and replicate by membrane growth and division out of pre-existing organelles.
[33] Peroxisomes also interact with the endoplasmic reticulum and cooperate in the synthesis of ether lipids (plasmalogens), which are important for nerve cells (see above).
