Enzyme Kinetics MCAT Practice Question
A 34-year-old man with a history of recurrent infections and progressive fatigue undergoes mitochondrial enzyme panel testing. Genetic sequencing reveals a mutation in the SDHA gene encoding succinate dehydrogenase (SDH). His fibroblasts are cultured and analyzed for enzymatic kinetics. When cells are incubated under aerobic conditions, SDH demonstrates Vmax of 100 nmol/min/mg and Km of 15 mM for succinate. When the same cells are exposed to hypoxic conditions (1% O2), Vmax decreases to 60 nmol/min/mg while Km remains 15 mM. The enzyme does not show cooperative binding. Which of the following best explains the kinetic changes observed under hypoxic conditions?
Answer choices
- AOxygen competitively inhibits succinate binding to the active site
- BHypoxia causes allosteric inhibition through accumulation of NADH and reduced ubiquinone
- CThe decrease in Vmax indicates oxygen is required as an electron acceptor for the catalytic cycleCorrect answer
- DSuccinate exhibits negative cooperativity in the hypoxic environment due to altered quaternary structure
- EKm would increase under hypoxia because succinate cannot be oxidized without O2 as a cofactor
- FThe mutation prevents SDH from functioning as Complex II, making oxygen a competitive substrate
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