Question

The digestive enzyme trypsin has a peak reaction rate at about 7.5 pH. Pepsin, an enzyme in the stomach, has a peak reaction rate at pH 2. Why does trypsin not work well at pH 2, and why does pepsin not work well at pH 7.5? Don’t just say because they are not their optimal pH.

Answer 1

Enzymes are most active at optimal pH, and any variation in pH beyond the optimal pH would cause a reduction in enzyme activity. Since the enzymes are proteins they have amino acids which have ionizable side chains. This is due to protonation of side chains in acidic pH and deprotonation in basic pH that alters the shape of the active site and the properties of the substrates too.

At pH 7.5 a number of active site amino acids are deprotonated in the pepsin rendering it less active

At pH 2 a number of active site amino acids are protonated in the trypsin rendering it less active