Glycolytic Enzyme Regulation and Deficiencies

A 3-year-old boy from rural Maharashtra presents with severe hypoglycemia (blood glucose 35 mg/dL), hepatomegaly, and lactic acidosis (pH 7.2, lactate 8 mmol/L) following a 6-hour fast. Clinical suspicion is high for a glycolytic enzyme deficiency. Which investigation is most specific for confirming phosphofructokinase (PFK) deficiency?

A 28-year-old woman with a history of recurrent muscle pain, myoglobinuria after exercise, and normal fasting glucose presents to the metabolic clinic. Serum CK is markedly elevated (8500 U/L). Suspicion is raised for pyruvate kinase (PK) deficiency. Which investigation is most appropriate to confirm the diagnosis?

A 28-year-old woman from Delhi presents with a 2-year history of recurrent episodes of severe muscle pain and weakness triggered by sustained exercise or fasting. During an acute episode, her serum creatine kinase is 8,500 U/L (normal <200), myoglobin is elevated, and urine is dark brown. A muscle biopsy shows subsarcolemmal glycogen accumulation. Genetic testing identifies a homozygous mutation in the PFKM gene (phosphofructokinase-muscle isoform). Which of the following best explains why her symptoms are exacerbated during sustained exercise?

During a biochemistry lecture on glycolytic regulation, the faculty discusses the most common site of allosteric regulation in glycolysis. Which enzyme represents the most important and most frequently regulated control point in the glycolytic pathway?

A 2-year-old girl from Tamil Nadu presents with severe hemolytic anemia, jaundice, and dark urine after eating fava beans. Blood film shows bite cells and Heinz bodies. Serum bilirubin is 6 mg/dL (predominantly indirect). Glucose-6-phosphate dehydrogenase (G6PD) activity is 2 U/g Hb (normal >5 U/g Hb). What is the most appropriate immediate next step?