Enzyme Kinetics MCAT Practice Question
A 34-year-old woman with a lifelong history of lactose intolerance presents to the gastroenterology clinic complaining of severe bloating and abdominal cramping after consuming dairy products. A research laboratory analyzes her intestinal lactase enzyme kinetics. When lactose concentration is increased from 2 mM to 20 mM in an in vitro assay, reaction velocity increases from 5 µM/s to 48 µM/s. At 200 mM lactose (mimicking a large dairy meal), the velocity plateaus at only 50 µM/s. Her enzyme has a measured Km of 10 mM. Which of the following best explains the plateau in reaction velocity observed at high substrate concentrations?
Answer choices
- AThe enzyme has reached its Vmax; all available enzyme molecules are saturated with substrateCorrect answer
- BSubstrate inhibition occurs at high lactose concentrations, competitively displacing enzyme-bound product
- CThe Km value increases at high substrate concentration due to allosteric conformational changes
- DAccumulated glucose and galactose products competitively inhibit further lactose hydrolysis
- EIntestinal lactase undergoes irreversible thermal denaturation at high substrate concentrations
- FHigh lactose concentration decreases the dissociation rate of the enzyme-substrate complex
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