zymogen granule

Definition

Target type: cellularcomponent

A membrane-bounded, cytoplasmic secretory granule found in enzyme-secreting cells and visible by light microscopy. Contain zymogen, an inactive enzyme precursor, often of a digestive enzyme. [GOC:jl, ISBN:0198506732]

Zymogen granules are membrane-bound organelles found in the cytoplasm of exocrine cells, primarily those involved in the secretion of digestive enzymes. They are essentially storage compartments for inactive precursor forms of digestive enzymes known as zymogens. These granules are spherical or ellipsoidal in shape and vary in size depending on the cell type. The composition of a zymogen granule is complex and includes a diverse array of proteins, including:

* **Zymogens:** These are the inactive forms of digestive enzymes such as pepsinogen, trypsinogen, chymotrypsinogen, and procarboxypeptidase. They are synthesized in the rough endoplasmic reticulum (RER) and transported to the Golgi apparatus where they are packaged into zymogen granules.
* **Membrane proteins:** The zymogen granule membrane is enriched with specific proteins that play a role in the targeting, docking, and fusion of the granule with the plasma membrane during secretion.
* **Other proteins:** In addition to zymogens and membrane proteins, zymogen granules may contain other proteins involved in the regulation of secretion, such as chaperones and proteases.

The internal environment of a zymogen granule is acidic, which helps to stabilize the zymogens and prevent their premature activation. This acidity is maintained by the presence of proton pumps embedded in the granule membrane.

During the process of secretion, zymogen granules translocate from the Golgi apparatus to the apical surface of the cell where they fuse with the plasma membrane. This fusion event releases the zymogens into the extracellular space, where they encounter the appropriate conditions for activation. For example, pepsinogen is activated to pepsin by the low pH of the stomach.

Overall, the zymogen granule is a crucial component of the exocrine secretory pathway, playing a critical role in the storage and regulated release of digestive enzymes. Its intricate composition and precise mechanisms of formation and secretion contribute significantly to the efficient digestion of food.'
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Proteins (2)

Compounds (6)