A 6-year-old boy of South Asian descent presents to the pediatric emergency department with acute hemolytic anemia, jaundice, and dark urine following ingestion of fava beans at a family meal. Peripheral blood smear shows Heinz bodies and bite cells. The enzyme marked **A** in the diagram is suspected to be deficient. Which of the following is the PRIMARY mechanism by which deficiency of this enzyme predisposes to hemolysis in this clinical scenario?