In glycolysis, what enzyme would be inhibited indirectly if intracellular glucose concentrations are very high?

• A. Glyceraldehyde-3-phosphate dehydrogenase
• B. Phosphofructokinase-1
• C. Pyruvate kinase
• D. Hexokinase

Answer: (A)

High intracellular glucose leads to buildup of glucose-6-phosphate, which feeds back to inhibit the first glycolysis step catalyzed by hexokinase. When that upstream step slows, the flow of carbon through glycolysis drops, so downstream intermediates like glyceraldehyde-3-phosphate become scarce. The enzyme that uses that substrate, glyceraldehyde-3-phosphate dehydrogenase, is effectively inhibited indirectly because its substrate concentration falls. The other enzymes are not being directly limited by the glucose level in this scenario, so this downstream effect best fits the question.