In glycolysis, which enzyme generates NADH while converting glyceraldehyde-3-phosphate to a high-energy intermediate?

• A. Hexokinase
• B. Glyceraldehyde-3-phosphate dehydrogenase (GAPDH)
• C. Phosphoglycerate kinase
• D. Pyruvate kinase

Answer: (B)

Glyceraldehyde-3-phosphate dehydrogenase is the enzyme that, during glycolysis, oxidizes glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate, a high-energy intermediate. In this step, NAD+ accepts a hydride, forming NADH, while an inorganic phosphate is added to create the high-energy acyl phosphate. This NADH production is specific to this step; the other enzymes do different tasks—hexokinase uses ATP to phosphorylate glucose, phosphoglycerate kinase uses 1,3-bisphosphoglycerate to generate ATP but does not produce NADH, and pyruvate kinase produces ATP from phosphoenolpyruvate later in glycolysis without forming NADH.