Digestive Enzymes In Lysosomes: 7 Facts You Should Know

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Lysosomes are cell organelle that helps in the degradation of proteins and nucleotides enclosed in a membrane. Let us see if lysosomes have digestive enzymes in them or not.

A few hydrolytic digestive enzymes are present in lysosomes like proteases, sulfatases and some glycosidases. These lysosomal enzymes are produced in the endoplasmic reticulum and transferred to the organelle.

The lysosome is surrounded by a single membrane which acts as a barrier between these degradative enzymes and the cell matrix. Because these enzymes are sometimes responsible for autophagy and cellular autolysis, lysosomes are also known as “suicidal bags of the cell”.

Let us discuss the number of digestive enzymes found in lysosomes, their functions when they release these digestive enzymes and many other related facts in this article.

How many digestive enzymes are found in lysosomes?

Multiple enzymes are found in lysosomes as they can digest proteins, DNA, RNA and other cell debris. Let us see the number of digestive enzymes found in lysosomes.

Almost 50 digestive enzymes are found inside lysosomes. They are useful in the decomposition of biological polymers like lipids, carbohydrates, and bacteria which prevent the cell from the intrusion of foreign materials.

A few of the digestive enzymes are mentioned below:

Serial No.GlycosidasesSulfatasesProteases
1.Lysosomal alpha-GlucosidaseSulfatase-2/SULF2Cathepsin V
2.Hyaluronan LyaseSulfamidase/SGSHCathepsin L
3.Heparinase I, II and IIIArylsulfatase A/ ARSACathepsin K
4.Galactosyl ceramidaseArylsulfatase B/ ARSBCathepsin H
5.O-GlycosidaseArylsulfatase G/ ARSGCathepsin F
6.Chitinase 3 like 1, 2 and 3Glucosamine (N-acetyl)-6-Sulfatase/GNSCathepsin D
7.Alpha galactosidase AIduronate 2-Sulfatase/IDSLysosomal Carboxypeptidase A
8.Beta, 1-3 galactosidaseN-Acetylgalactosamine-6-Sulfatase/GALNSNapsin A
9.Alpha-N-acetylgalactosaminidase/NAGA                     –Legumain/Asparaginyl Endopeptidase
10.Alpha-L-Fucosidase                    –Galactosylceramidase/GALC
Digestive enzymes found in lysosomes

What are the functions of digestive enzymes in lysosomes?

Lysosomes are subcellular compartments containing digestive enzymes which are degradative and hydrolytic. Let us discuss its function in the lysosome.

The main function of lysosomal enzymes is the breakdown of large molecules into simpler ones. These macromolecules are stored in the cells, which are called lysosomal storage cells. Lysosomal enzymes are also known as acid hydrolases.

Listed below are some of the functions of digestive enzymes:

  • They are majorly involved in breaking down and engulfing the materials taken up by the cell through endocytosis.
  • These enzymes also take place in phagocytosis and autophagy.
  • As specialised cells, macrophages are the main site for the degradation of large molecules like cell debris, bacteria or some other biological components to eliminate them outside the cell.
  • These materials get associated and engorged by phagosomes in the form of vesicles and get fused with lysosomes to form “phagolysosome” and digests unwanted materials.
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Lysosomes Image credit: Wikimedia commons

When do lysosomes release digestive enzymes?

As the synthesis of digestive enzymes involves three cellular components- Golgi sacs, ER and lysosomes, it is termed GERL. Let us discuss when lysosomes release digestive enzymes.

Lysosomes release enzymes after complete maturation. After the production of enzymes in RER, it gets transported to the trans-Golgi network (TGN) and fuses with the lysosomes.

How do lysosomes release digestive enzymes?

If a cell ingests something from the extracellular environment, any biomolecules, pathogens, or secretory pathways via autophagocytotic, get triggered and release the enzymes simultaneously by rupturing the membrane and performing the task by engulfing the foreign invaders. Cells would be destroyed and molecules converted into a simple form that can be reutilised.

Where are digestive enzymes of lysosomes produced?

Lysosomal enzymes are mainly found in the acidic environment causing the breakdown of macromolecules. Let us explore where they are produced.

Digestive enzymes of lysosomes are produced in the endoplasmic reticulum. These are active at acidic pH (approx. 5) that can hydrolyse proteins, polysaccharides and other nucleotides. These enzymes are called hydrolytic enzymes.

After synthesizing, these enzymes go towards the Golgi machinery and form the vesicle, which is getting tagged by mannose-6-phosphate and is incorporated with the lysosomes.

Why do digestive enzymes not digest lysosomes?

Digestive enzymes provide safety against foreign particles because of their acidic pH. Let us see why they do not digest lysosomes.

Digestive enzymes cannot digest lysosomes because of high glycosylation in their surrounding membrane. They have a protective layer made by glycocalyx as well as vacuolar-type H+ ATPase which prevents them from internal damage.

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Structure of glycocalyx
Image credit: Wikimedia commons

How do lysosomes digest food?

Lysosomes are helpful in the digestion of foreign particles and eat up the dead cell organelles to maintain cleanliness inside a cell. Let us explore how lysosomes digest food.

Lysosomes are having hydrolytic enzymes which can digest food. They act upon the polymers of biomolecules. As they play a major role in the digestive system of some protists, which can convert the larger food molecule into an absorbable form.

How do lysosomes digest food?

Lysosomes digest food because they are the principal site for intracellular digestion. Some enzymes like Acid phosphodiesterase acts upon Oligonucleotides, Acid deoxyribonuclease acts upon DNA, β- Glucuronidase digests Polysaccharides and mucopolysaccharides, α–Mannosidase helps in the breakdown of Mannosides, glycoproteins etc.

These digestive enzymes bind to the substrate at optimum temperature and pH which facilitates the breakdown of polysaccharides and other molecules.

How do lysosomes digest bacteria?

Lysosomes are the cleaning system of the cell as they remove dead cell organelle, and participate in intracellular and extracellular digestion.

Lysosomes digest bacteria by forming vesicles filled with digestive enzymes. If any bacteria or antigen enter the cell, the plasma membrane gets pinched off and forms a closed vesicle, transported to the Golgi network and fuses with lysosomes having hydrolytic enzymes.

After enzymatic digestion, the undigested material is stored in a vacuole structure and eliminated from the body. They perform autophagy by digesting the bacterial components and degrading their genetic material by nucleosidase. But the decomposition of viruses is quite a tough task. These actions are mainly responses due to cell starvation, immune defence and other cellular stress.

Conclusion

In this article, we have discussed the number of digestive enzymes found in lysosomes, their functions, why digestive enzymes are not digested in lysosomes etc. Lysosomes are spherical and are found in animals. It is able to protect the cell with its own digestive enzymes but if it leaks, somehow, cytosolic pH is sufficient to inactive the enzymes due to its alkaline pH which is equal to 7.2.

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