In substrate inhibition, how does enzyme activity respond to increasing substrate concentration at high levels?

In substrate inhibition, how does enzyme activity respond to increasing substrate concentration at high levels?

• A. Increases linearly
• B. Decreases after an optimum
• C. Plateaus
• D. Increases exponentially

Answer: (B)

Substrate inhibition shows that enzyme activity can fall when substrate levels get very high. At moderate substrate concentrations, the enzyme works faster as more substrate is available, but beyond some optimum concentration, an extra substrate molecule can bind to a second (inhibitory) site or interfere with catalysis. This forms an inactive or less active complex, so the turnover rate decreases even as more substrate is present. That creates a peak in activity and a decline at high substrate levels. The other patterns—continuous linear rise, a simple plateau, or an exponential increase—don’t reflect the inhibitory interaction that happens when substrate concentration becomes very large.

Substrate inhibition shows that enzyme activity can fall when substrate levels get very high. At moderate substrate concentrations, the enzyme works faster as more substrate is available, but beyond some optimum concentration, an extra substrate molecule can bind to a second (inhibitory) site or interfere with catalysis. This forms an inactive or less active complex, so the turnover rate decreases even as more substrate is present. That creates a peak in activity and a decline at high substrate levels. The other patterns—continuous linear rise, a simple plateau, or an exponential increase—don’t reflect the inhibitory interaction that happens when substrate concentration becomes very large.