Which two enzymes of the pentose phosphate pathway catalyze production of NADPH?

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11ecba2d_0e57_0009_a3bf_07f4ebdb2248_MD0008_00 The pentose phosphate pathway consumes glucose 6-phosphate to produce ribose 5-phosphate for nucleotide synthesis and NADPH for use in lipid synthesis and antioxidative processes. Excess ribose 5-phosphate is converted into the glycolysis intermediates fructose 6-phosphate and glyceraldehyde 3-phosphate. These intermediates can then be recycled back into the pentose phosphate pathway to produce more NADPH, or into glycolysis to generate ATP. Oxidoreductases interconvert NAD⁺ and NADH, NADP⁺ and NADPH, or FAD and FADH₂ by transferring hydride ions or hydrogen atoms. They frequently have the word "dehydrogenase" in their names. Glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase are the only oxidoreductases in the pentose phosphate pathway; they transfer hydride ions from glucose 6-phosphate and 6-phosphogluconate to NADP⁺. These enzymes generate the majority of the NADPH in a cell. (Choice A) Ribose 5-phosphate isomerase and ribulose 5-phosphate epimerase isomerize ribulose 5-phosphate to ribose 5-phosphate and xylulose 5-phosphate, respectively. They occur in the nonoxidative phase of the pentose phosphate pathway and do not generate NADPH. (Choice B) Transketolase and transaldolase transfer carbons from one sugar phosphate to another, ultimately regenerating the glycolysis intermediates fructose 6-phosphate and glyceraldehyde 3-phosphate. They do not participate in NADPH synthesis. (Choice D) Lactonase hydrolyzes 6-phosphogluconolactone to form 6-phosphogluconate without generating NADPH. Aldolase is part of glycolysis and gluconeogenesis, but not the pentose phosphate pathway. Educational objective: The pentose phosphate pathway generates ribose 5-phosphate and NADPH. The NADPH is generated by reduction of NADP⁺, which is catalyzed by the oxidoreductases glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase.

Which Two Enzymes of the Pentose Phosphate Pathway Catalyze Production