In the HMP shunt, the IRREVERSIBLE oxidative phase generates NADPH and ribulose-5-phosphate. The enzyme that regenerates glucose-6-phosphate from the non-oxidative phase intermediates is:
- A Phosphoglucose isomerase, which directly converts ribulose-5-P to G-6-P
- B Transketolase and transaldolase, which rearrange C5 phosphates to regenerate F-6-P and G-3-P, which are converted to G-6-P by gluconeogenic/glycolytic enzymes ✓
- C Glucose-6-phosphate dehydrogenase running in reverse, regenerating NADP+
- D Phosphoglucomutase, converting G-1-P to G-6-P
Correct answer: B. Transketolase and transaldolase, which rearrange C5 phosphates to regenerate F-6-P and G-3-P, which are converted to G-6-P by gluconeogenic/glycolytic enzymes
Explanation
The non-oxidative phase of the HMP shunt uses transketolase (thiamine-dependent) and transaldolase to interconvert C3, C4, C5, C6, and C7 phosphate sugars. The net result can be the conversion of 3 × ribulose-5-P → 2 × F-6-P + G-3-P; these are then converted to G-6-P via phosphoglucose isomerase and the gluconeogenic enzyme fructose-1,6-bisphosphatase and phosphoglucose isomerase (or reversed glycolysis). This allows cells to tailor NADPH vs ribose-5-P production based on requirements.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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