Pentavalent arsenate added to an in vitro glycolysate allows conversion of glucose to pyruvate, yet the measured net ATP production falls to zero. At which step is ATP generation specifically abolished?

• A Phosphoglycerate kinase reaction, because 1-arseno-3-phosphoglycerate hydrolyses spontaneously ✓
• B Hexokinase reaction, because glucose-6-arsenate forms instead of glucose-6-phosphate
• C Pyruvate kinase reaction, because phosphoenolpyruvate cannot form
• D Phosphoglucose isomerase reaction, because the substrate becomes unstable

Explanation

Arsenate substitutes for inorganic phosphate at glyceraldehyde-3-phosphate dehydrogenase, forming 1-arseno-3-phosphoglycerate. This mixed anhydride hydrolyses spontaneously before phosphoglycerate kinase can act, so the ATP normally made at that substrate-level phosphorylation step is lost. Glycolysis itself continues to pyruvate because the carbon flow is intact, only energy capture fails. The other named reactions are unaffected.

Reference: Lehninger Principles of Biochemistry, 8th ed.

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