Why does the enzyme trypsin get deactivated when introduced in gastric juice of stomach?

Trypsin is an enzyme that plays a crucial role in the digestion of proteins in the human body. It is produced by the pancreas and secreted into the small intestine, where it breaks down proteins into smaller peptides and amino acids. However, trypsin gets deactivated when introduced into the gastric juice of the stomach due to the following reasons:

1. Low pH: The gastric juice in the stomach is highly acidic, with a pH ranging from 1 to 2. Trypsin has an optimal pH range between 7 and 9. The extremely low pH of gastric juice denatures trypsin, causing it to lose its structure and catalytic activity.

2. Presence of Pepsin: The stomach also secretes another enzyme called pepsin, which is responsible for the initial breakdown of proteins in the acidic environment of the stomach. Pepsin functions best at a low pH and can directly degrade trypsin, further contributing to its deactivation.

3. Inactivation by Acidic Proteases: Gastric juice contains various acidic proteases, such as cathepsin D and gastricsin, which can directly target and cleave the peptide bonds within the trypsin molecule, leading to its inactivation.

4. Protease Inhibitors: The stomach also produces protease inhibitors, which are proteins that specifically bind to and inhibit the activity of proteolytic enzymes like trypsin. These inhibitors prevent trypsin from carrying out its catalytic functions.

5. High Enzyme Concentration: In the pancreas, trypsin is synthesized as an inactive precursor called trypsinogen to prevent its premature activation within the pancreas itself. However, when trypsinogen enters the small intestine, it gets activated by another enzyme called enterokinase. In contrast, the high concentration of trypsin in the gastric juice might lead to autoactivation of trypsinogen, resulting in its rapid inactivation due to the acidic conditions and the presence of inhibitors.

Therefore, the combination of low pH, the presence of pepsin and other acidic proteases, protease inhibitors, and the high enzyme concentration in the gastric juice leads to the deactivation of trypsin when introduced into the stomach. This ensures that trypsin remains inactive and does not interfere with the digestion of proteins in the stomach, which is primarily carried out by pepsin.