Depression of an enzyme system is caused by

• A. Increased enzyme production
• B. Genetic mutation
• C. Environmental temperature changes
• D. Caused by a drug competing for the same enzymes as another substance or even food

Answer: (D)

Depression of an enzyme system occurs most clearly when a substance blocks the enzyme by competing with its normal substrate for the active site. A drug that binds to that active site prevents the substrate from binding, slowing the reaction and reducing the enzyme’s overall activity. This is competitive inhibition, a common way drugs interact with enzymes, especially those like the cytochrome P450 family that metabolize many substances. When a drug competes for the same enzymes as another substance or even food, it can decrease the metabolism of that substance, effectively depressing the enzyme system.

Increasing enzyme production would boost capacity rather than depress it, a genetic mutation might reduce function but isn’t the typical scenario described here, and environmental temperature changes alter reaction rates in a general way rather than through direct competitive inhibition.