Metabolic Pathways and Regulation · USMLE Step 1

Which enzyme catalyzes the rate-limiting step of glycolysis and is strongly regulated by cellular energy status?

  1. Hexokinase
  2. Phosphofructokinase-1 (PFK-1)
  3. Pyruvate kinase
  4. Glyceraldehyde-3-phosphate dehydrogenase
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Correct answer: Phosphofructokinase-1 (PFK-1)

PFK-1 catalyzes the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate and acts as the major regulatory checkpoint in glycolysis. Its activity is modulated by allosteric effectors like ATP, ADP/AMP and citrate, reflecting the energy status of the cell.

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