MCAT Biochemistry Question 136: Answer and Explanation
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Question: 136
1. During a myocardial infarction, the oxygen supply to an area of the heart is dramatically reduced, forcing the cardiac myocytes to switch to anaerobic metabolism. Under these conditions, which of the following enzymes would be activated by increased levels of intracellular AMP?
- A. Succinate dehydrogenase
- B. Phosphofructokinase-1
- C. Isocitrate dehydrogenase
- D. Pyruvate dehydrogenase
Correct Answer: B
Explanation:
Phosphofructokinase-1 (PFK-1), which catalyzes the rate-limiting step of glycolysis, is the only enzyme listed here that functions under anaerobic conditions. The other enzymes are all involved in the oxygen-requiring processes discussed in this chapter. Succinate dehydrogenase, choice (A), appears in both the citric acid cycle and as part of Complex II of the electron transport chain. Isocitrate dehydrogenase, choice (C), catalyzes the rate-limiting step of the citric acid cycle. Pyruvate dehydrogenase, choice (D), is one of the five enzymes that make up the pyruvate dehydrogenase complex.