Pentose Phosphate Pathway of Glucose Oxidation:- The Oxidative Phase Produces Pentose Phosphates and NADPH
The first reaction of the pentose phosphate pathway (Fig. 14–21) is the oxidation of glucose 6-phosphate by glucose 6-phosphate dehydrogenase (G6PD) to form 6-phosphoglucono--lactone, an intramolecular ester. NADP is the electron acceptor, and the overall equilibrium lies far in the direction of NADPH formation. The lactone is hydrolyzed to the free acid 6-phosphogluconate by a specific lactonase, then 6-phospho gluconate undergoes oxidation and decarboxylation by 6-phosphogluconate dehydrogenase to form the ketopentose ribulose 5-phosphate. This reaction generates
FIGURE 14–21 Oxidative reactions of the pentose phosphate path way. The end products are ribose 5-phosphate, CO2, and NADPH.
a second molecule of NADPH. Phosphopentose isomerase converts ribulose 5-phosphate to its aldose iso mer, ribose 5-phosphate. In some tissues, the pentose phosphate pathway ends at this point, and its overall equation is
Glucose 6-phosphate+2NADP+H2O→ribose 5-phosphate+CO2+2NADPH+2H+
The net result is the production of NADPH, a reductant for biosynthetic reactions, and ribose 5-phosphate, a precursor for nucleotide synthesis.
