Peroxisomes | Definition, Functions, Types, Structure, Discovered!

Hello friends, in this article we will know what is peroxisomes, and will also learn about it: Its Definition, Types, Structure, Discovered, functions, etc. So let’s start without wasting time.

What are peroxisomes?

The peroxisome is a cell organelle.

Where is found peroxisome?

Peroxisomes are found in all Eukaryotic cells. These were first observed by Rhodin (1954)  in kidney cells of rats and were named peroxisomes by Christian de Duve in 1965.

Peroxisome structure –

Peroxisomes are microbodies having a diameter of 0.5–1.5 nm. These are bounded by single membranes and enclosed enzymes peroxidases and catalase, And carry out oxidative reactions using molecular oxygen. They produce hydrogen peroxide through their degradative activity.

The enzymes present are –

1. Uric acid oxidase
2. D-amino acid oxidase
3. Hydrolytic acid oxidase
4. NADH-glyoxylate reductase
5. NADP-isocitrate dehydrogenase
6. Catalase.

Peroxisomes function –

Peroxisomes are associated with the following activities.

1. Oxidation or respiration: Like mitochondria, peroxisome also helps in cell respiration. In green plants, this carries out photorespiration. The peroxisomal enzymes are of two types: 
   • Peroxisomal oxidase catalyses the Oxidation of a variety of substrates and transfers hydrogen atoms to molecular oxygen for hydrogen peroxide (H₂O₂). H₂O₂ is highly toxic.
   • Peroxisomal catalase enzyme immediately breaks down H₂O₂ to H₂O  and oxygen or uses H₂O₂ to oxidize substances like phenol formic acid formaldehyde and alcohol etc.
2. Permeability: The membrane binding the peroxisome is highly permeable. It allows inorganic ions and substances with low molecular weight to pass through its membrane.
3. Detoxification: Peroxisomal enzymes detoxify various molecules in the liver and kidney and protect the body from different toxins.
4. Metabolism of fatty acid: peroxisomal enzymes catalyse the breakdown of fatty acid to acetyl CoA, which enters mitochondria to start the citric acid cycle or Krebs cycle.

Glyoxysomes –

Glyoxysomes are similar to peroxisomes, but they contain enzymes of the glyoxylate cycle along with peroxisomal enzymes. These were described by R. W. Briedenback in 1967. These are present in plant tissues.

The enzymes present in glyoxysomes are isocitrate lyase and malate synthetase and several essential enzymes of the Krebs cycle. During the germination of seeds, the fat stored in the endosperm is transformed into carbohydrates by the way of the glyoxylate cycle-a modified form of the Krebs cycle.

The glyoxylate cycle does not occur in animal cells. They are unable to convert fatty acids into carbohydrates.

Spherosomes –

The spherosomes are spherical particles about 0.5 to 2.5 microns in diameter. These occur in most plant cells. These originate from ER and contain lipids and proteins. Basically, the spherosomes associated with the synthesis and storage are associated with the synthesis and storage of lipids.

In maize root and tobacco endosperm tissue, these are rich in hydrolytic enzymes like acid phosphatase and are considered to be lysosomes, but their lipid nature makes them distinct from the lysosomes. Spherosomes do not exhibit a wide range of lytic action as lysosomes.

Difference between Peroxisomes and Glyoxysomes –

Peroxisomes	Glyoxysomes
It is found in animal cells and leaves of higher plants.	It is found in plant cells and are abundant in the endosperm of germinating seeds.
Contain enzymes-peroxidases and catalyses.	Contain enzymes peroxidases catalases and enzymes of the glyoxylate cycle.
Carry out photorespiration.	Are associated with triglyceride metabolism.
In peroxisomes, hydrogen atoms are oxidized to hydrogen peroxide (H2O2) which is degraded into H2O and oxygen.	Transform stored fat into carbohydrates by the glyoxylate cycle.

Difference between Peroxisomes and Lysosomes –

Peroxisomes	Lysosomes
It is found in animal cells and in the leaves of higher plants.	It is found in animal cells and a few plant cells.
Contain peroxidases and catalase enzymes.	Contain tissue dissolving of hydrolytic enzymes.
Carry out photorespiration in green plants.	It is responsible for the hydrolysis of organic molecules and the dissolving of Hydrolytic enzymes.
Help in the release of energy.	Help in intracellular digestion or cell dissolution.

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