ADVERTISEMENTS:
Useful notes on the Origin of Lysosomes!
They have multiple origins depending upon the tissue in which they are located or on their function in a specific cell.
1. Extracellular origin:
Lysosomes may be the vacuoles absorbed into cell by the process, pinocytosis. Pinocytic vacuole may later become cytoplasmic particle and thereon enzymatic activity becomes developed.
Image Courtesy : http://media-2.web.britannica.com/eb-media/38/8038-050-75518CEA.jpg
2. Origin from Golgi complex:
There are evidences that lysosomes originate from Golgi complex and represent zymogen granules. Their similar function and structure with Golgi bodies support this view. Recent studies have shown that accumulation of secretory products within Golgi vacuoles leads to the formation of lysosomes, and that the membranes surrounding the products are derived from Golgi membranes.
Thus a portion of the Golgi apparatus is converted into lysosomal particles during the secretory process and evidence indicates that the change is accompanied by an alteration of enzymatic activity, since Golgi membranes do not ordinarily contain acid phosphatase. Starved Euglena, for example, develop large numbers of lysosomes in the Golgi region, which exhibits high acid phosphatase activity.
Table 1. Acid hydrolytic enzymes of lysosomes:
| Enzyme | Substrate | Product |
| 1. Nucleases | Polynucleotides | Bases + phosphate + pentose |
| Acid ribonuclease deoxyribonuclease | RNA | Bases + phosphate + ribose Bases + phosphate + deoxyribose. |
| Acid | DNA | |
| 2. Phosphatases | ||
| Acid phosphatase | Phosphate monoesters | Orthophosphate and product |
| Phosphoprotein | ||
| phosphatase | Phosphoprotein | Orthophosphate and protein |
| 3. Proteases | ||
| Cathepsin | Polypeptides | N-Terminal dipeptides |
| Collagenase | Collagen | Proline, amino acids |
| 4. Glycosidases | ||
| α -glucosidase | α-D-glucosides chitobiose | Alcohol and D-glucose Two acetylamine-2-deoxy- D-glucose |
| β-N-acetylglucosamine hydrolase | β-D-glucoronides | Alcohol and D-glucoronic acid |
| β. glucoronidase | β-D-galactosides | Alcohol and D-galactose |
| β-galactosidase | α-D-mannosides | Alcohol and D-mannose |
| α-mannosidase | ||
| 5. Sulphatases | ||
| Arylsulphatase | Phenol sulphate | Phenol and H2SO4 |
| 6. Lipase | Lipids | Fragments |
3. Origin from ER:
Novikoff (1965) reported that lysosomes originate directly from granular endoplasmic reticulum. Protein granules are often seen in enlargements of ER, which, if pinched off would produce lysosomes (Pitt, 1975).
