Question 22.3: Factors Influencing Enzyme Activity Lactase catalyzes the fo...
Factors Influencing Enzyme Activity
Lactase catalyzes the following reaction:
Lactose + \text{H}_{2}\text{O} → Glucose + Galactose
What would be the effect on the activity of lactase of each of the following?
(a) Raising the pH to 12
(b) Raising the concentration of lactose
(c) Raising the concentration of lactase
(a) From Table 22.2, we can see that the pH optimum for lactase is 6.0. Therefore, raising the pH to 12 would deactivate the enzyme, perhaps irreversibly.
| Table 22.2 Optimum pH Range for Certain Enzymes | |||
| Optimum pH | Substrate | Location | Enzyme |
| 1.5–2.0 | Peptide bonds | Stomach | Pepsin |
| 6 | Lactose | Small intestine | Lactase |
| 6.7–7.0 | Amylose | Pancreas | Amylase |
| 7.7–8.0 | Peptide bonds | Small intestine | Trypsin |
| 8 | Lipid ester bonds | Pancreas | Lipase |
| 9.7 | Arginine | Liver | Arginase |
(b) From Figure 22.3, we can see that, in general, raising the concentration of the substrate increases the activity. However, to fully answer this question, we would have to know where on the curve we are to begin with. If the concentration of substrate is already at saturating levels, then raising it more would not change the activity.
(c) From Figure 22.2, we see a linear response to the reaction rate with concentration of enzyme. Therefore, raising the concentration of lactase will increase the activity in a linear fashion.
■ Quick Check 22.3
If we know that an enzyme with an optimal pH of 7.0 has a critical histidine in its active site that helps catalyze a reaction, what is one likely reason that lowering the pH to 5.0 would deactivate the enzyme?
