A 35-year-old farmer presents to the emergency department with acute onset of severe muscle weakness, tachycardia, and hypotension following accidental exposure to an insecticide containing inorganic arsenic. Laboratory studies show profound hypoglycemia and markedly elevated lactate levels. The structure marked **D** in the glycolysis pathway diagram is the primary target of arsenic toxicity in this patient. Which of the following best explains the mechanism by which arsenic impairs the function of this enzyme and leads to the observed metabolic derangement?