| NADPH is synthesized by two dehydrogenases, in the first and third reactions of the pentose phosphate pathway (Fig. 11.9). In the first step of the pathway, the Glc-6-P dehydrogenase (G6PDH) reaction produces NADPH by oxidation of Glc-6-P to 6-phosphogluconic acid lactone, a cyclic sugar ester. The lactone is hydrolyzed to 6-phosphogluconic acid by lactonase. Oxidative decarboxylation of 6-phosphogluconate, catalyzed by 6-phosphogluconate dehydrogenase, then yields the ketose sugar, ribulose 5-phosphate, plus 1 mole of CO2 and the second and final mole of NADPH.
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