Microbodies

Microbodies are small, single‑membrane‑bound organelles present in eukaryotic cells, including plants, animals, fungi, and protozoa. They range from approximately 0.2 to 1.5 micrometres in diameter and are visible only under electron microscopy. These organelles lack genetic material and are rich in specific enzymes that facilitate oxidative metabolism, detoxification, and other vital cellular functions.

1.0Types of Microbodies

1. Peroxisomes

• Found in almost all eukaryotic cells, especially abundant in liver and kidney tissues. 
• Named by Christian de Duve, they generate and degrade hydrogen peroxide. 
• Contain oxidative enzymes, such as oxidases and catalase, to neutralise H₂O₂. 
• Key roles include lipid metabolism, detoxification of harmful substances, and the management of reactive oxygen species.

2. Glyoxysomes

• Specialised peroxisomes in fat‑storing tissues of germinating seeds (e.g., castor, groundnut) and some fungi.
• Contains enzymes of the glyoxylate cycle (isocitrate lyase, malate synthase) along with peroxisomal enzymes. 
• Convert stored lipids into carbohydrates via β‑oxidation to acetyl‑CoA, then through the glyoxylate cycle for gluconeogenesis.
• After lipid mobilisation, glyoxysomes may transform into peroxisomes and later reappear during senescence.

3. Spherosomes

• Present only in plant cells, especially oil‑storing tissues like endosperm. 
• Bounded by a phospholipid monolayer (“half‑unit” membrane) with hydrophilic heads outward. 
• Primarily store and synthesise lipids; some also exhibit hydrolytic (lysosome‑like) activity. 

4. Glycosomes (in protozoa)

• Found in organisms like Trypanosoma and Leishmania.
• Contain glycolytic enzymes that facilitate glucose metabolism in these protozoans. 

5. Woronin Bodies (in fungi)

• Dense-core microbodies derived from peroxisomes are present in filamentous Ascomycota. 
• Function to seal septal pores following hyphal damage to prevent cytoplasmic leakage. 

2.0Structure & Biogenesis of Microbodies

• All microbodies are spherical or ovoid vesicles, 0.2–1.5 µm in diameter, with a single phospholipid bilayer membrane (or monolayer in spherosomes). 
• They contain a granular, fibrillar, or crystalloid matrix that is rich in specific enzymes but lacks DNA. 
• Biogenesis begins in the endoplasmic reticulum, where vesicles bud and mature into microbodies; enzyme targeting is mediated by peroxisomal targeting sequences (PTS). 

3.0Microbodies Functions

• Peroxisomes
• Detoxify harmful compounds like alcohol, phenols, formaldehyde, and xenobiotics. 
• Carry out β‑oxidation of fatty acids, producing acetyl‑CoA and H₂O₂; catalase converts H₂O₂ to water and oxygen. 
• In plants, they participate in photorespiration by metabolising glycolate produced in chloroplasts into glyoxylate, glycine, and serine.
• Synthesise plasmalogens essential for brain and lung function in mammals. 
• Glyoxysomes
• Enable conversion of lipids to carbohydrates during seed germination—a vital energy source before photosynthesis begins. 
• Work in tandem with spherosomes and mitochondria to channel fats into the formation of sugar. 
• Spherosomes
• Serve as lipid storage and synthesis centres; some possess hydrolytic enzymes for limited digestion.
• Glycosomes
• Central to glycolysis in certain protozoa, ensuring energy production and metabolic intermediates. 
• Woronin Bodies
• Protect fungal cells by blocking septal pores upon injury.

4.0Microbodies Examples

Microbodies are small, membrane-bound organelles found in eukaryotic cells, and they include several important types based on their enzymatic function and location. 

1. Peroxisomes

• Found in animal and plant cells.
• Contain enzymes like catalase and oxidases.
• Involved in the detoxification of hydrogen peroxide and fatty acid oxidation.

2. Glyoxysomes

• Found mainly in plant cells, especially in germinating seeds.
• The enzymes of the glyoxylate cycle, like isocitrate lyase and malate synthase, are contained.
• Convert stored fats into carbohydrates during seed germination.

3. Hydrogenosomes (in some anaerobic eukaryotes)

Enzymes in the glyoxylate cycle, such as isocitrate lyase and malate synthase, are involved in energy metabolism, producing hydrogen, ATP, and acetate.

4. Glycosomes (in certain protozoa, like Trypanosoma)

The system contains enzymes for glycolysis, allowing sugar metabolism in specialised compartments.

5.0Difference Between Peroxisomes and Glyoxysomes