In the HMP (pentose phosphate) pathway, glucose-6-phosphate dehydrogenase produces NADPH. Which step of the non-oxidative phase regenerates fructose-6-phosphate and glyceraldehyde-3-phosphate, and what enzyme primarily catalyzes these reversible interconversions?

• A 6-Phosphogluconate dehydrogenase produces NADPH and ribulose-5-phosphate; transketolase regenerates glycolytic intermediates
• B Transketolase and transaldolase mediate carbon-group transfers linking pentose phosphates to fructose-6-phosphate and glyceraldehyde-3-phosphate ✓
• C Ribulose-5-phosphate isomerase converts ribulose-5-phosphate directly to fructose-6-phosphate
• D Phosphofructokinase-2 converts ribose-5-phosphate to fructose-2,6-bisphosphate

Explanation

In the non-oxidative phase of the HMP shunt, transketolase (thiamine-PPi dependent) and transaldolase transfer 2-carbon and 3-carbon units respectively among pentose phosphates, ultimately regenerating fructose-6-phosphate and glyceraldehyde-3-phosphate that can enter glycolysis. This allows the pathway to be balanced for NADPH production when pentose demand is low. Transketolase activity in red cells is used clinically to detect thiamine deficiency.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

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