Question

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

Answer 1

Can't handle the pH Gastric juice is fairly acidic, and very acidic conditions have detrimental consequences on enzymes, often times denaturing them and messing with their function and making them deactive.

Answer 2

at the active site trypsin uses the catalytic triad "histidine-aspartate-serine" to carryout proteolytic activity, lowering the pH would render the system unable to perform as it normally does. Also, just like any other protein, protonation of susceptible sites would change the native conformation of the enzyme reducing or eliminating it's activity.