Enzyme Kinetics MCAT Practice Question
A 45-year-old man with type 2 diabetes presents for evaluation of a new antidiabetic agent currently in clinical trials. The drug is designed to inhibit hexokinase, the first enzyme in the glycolytic pathway. In vitro kinetic studies reveal that the drug binds to hexokinase at a site distinct from the glucose-binding pocket. Researchers observe that when hexokinase enzyme concentration is doubled in the assay medium containing the inhibitor, the reaction velocity increases proportionally to the increased enzyme concentration. The inhibitor's effect on enzyme kinetics is independent of substrate (glucose) concentration at physiologically relevant ranges. Which of the following best describes the mechanism by which this inhibitor affects hexokinase kinetics?
Answer choices
- AThe inhibitor competitively blocks the glucose-binding site and can be overcome by increasing substrate concentration
- BThe inhibitor decreases both Vmax and Km proportionally, making it clinically ineffective regardless of enzyme concentration
- CThe inhibitor decreases Vmax without significantly altering KmCorrect answer
- DThe inhibitor increases Km while leaving Vmax unchanged, requiring higher glucose concentrations for enzyme saturation
- EThe inhibitor binds irreversibly to hexokinase and cannot be displaced even with excess enzyme molecules
- FThe inhibitor selectively binds only to the enzyme-substrate complex and not to free enzyme
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