Protease Activation
Let's now address protease activation.
- Recall, that, like in the stomach, pancreatic proteases are stored and secreted as inactive precursor enzymes (zymogens).
- Their storage as zymogens protects acinar cells from autodigestion.
- Draw a longitudinal cross section of the duodenum – the location of enzyme activation and subsequent action.
- Indicate the mucosal layer, whose epithelial cells interface the duodenal lumen.
- We omit the other layers for clarity.
- Show the inactive proteases (eg, chymotrypsinogen) and, specifically, the inactive trypsinogen, (which are secreted by the pancreas) in the duodenal lumen.
- Show proteolytic enzyme enterokinase, and indicate it is bound to the duodenal epithelium plasma membrane.
- Indicate that it converts trypsinogen to its active form trypsin.
- Next, show that trypsin, which is itself another proteolytic enzyme, activates the precursor zymogens (such as chymotrypsinogen) to their active protease forms (chymotrypsin).
- Trypsin activates pancreatic zymogens by cleaving them into their active proteases.
- These proteases can now themselves break down proteins.
- Note that pancreatic amylase, lipase, and nucleases are released in their active form.
Protease Activation
Like in the stomach, pancreatic proteases are stored and secreted as inactive precursor enzymes (zymogens). Their storage as zymogens protects acinar cells from autodigestion.
- Duodenum = the location of enzyme activation and subsequent action.
- Inactive proteases (eg, chymotrypsinogen) and, specifically, the inactive trypsinogen, (which are secreted by the pancreas) in the duodenal lumen.
- Proteolytic enzyme enterokinase (bound to the duodenal epithelium plasma membrane).
- Trypsin, which is itself another proteolytic enzyme, activates the precursor zymogens (such as chymotrypsinogen) to their active protease forms (chymotrypsin).
Note that pancreatic amylase, lipase, and nucleases are released in their active form.