The pentose phosphate pathway (PPP) is activated in response to oxidative stress. The REGULATORY enzyme controlling flux through the PPP is inhibited by its own product. Which substrate-product pair is involved in this feedback regulation?
- A Glucose-6-phosphate dehydrogenase is inhibited by NADPH ✓
- B 6-phosphogluconate dehydrogenase is inhibited by ribulose-5-phosphate
- C Transketolase is inhibited by elevated NADH
- D G6PDH is activated by NADP+ and product-inhibited by ATP
Correct answer: A. Glucose-6-phosphate dehydrogenase is inhibited by NADPH
Explanation
Glucose-6-phosphate dehydrogenase (G6PDH) catalyses the first and rate-limiting step of the PPP, converting G6P to 6-phosphogluconolactone while reducing NADP+ to NADPH. NADPH is a competitive inhibitor of G6PDH — when cellular NADPH is high (low oxidative stress), the PPP slows; when NADPH is consumed combating oxidative stress (regenerating GSH via glutathione reductase), NADPH falls, relieving inhibition and accelerating the PPP. This exquisite feedback precisely matches NADPH production to cellular redox needs.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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