Catalyzes the rate-limiting step of the oxidative pentose-phosphate pathway, which represents a route for the dissimilation of carbohydrates besides glycolysis. The main function of this enzyme is to provide reducing power (NADPH) and pentose phosphates for fatty acid and nucleic acid synthesis (By similarity). D-glucose 6-phosphate + NADP(+) = 6-phospho-D-glucono-1,5-lactone + H(+) + NADPH Carbohydrate degradation; pentose phosphate pathway; D-ribulose 5-phosphate from D-glucose 6-phosphate (oxidative stage): step 1/3. Shows growth defects in acetate-supplemented medium; the phenotype is enhanced by addition of hydrogen peroxide (increased oxidative stress) and/or double knockout of ZWF1 and YHM2 (PubMed:20371607). Decreases the cytosolic NADPH/NADP(+) ratio; this effect is enhanced in the presence of hydrogen peroxide (PubMed:20371607). Ribitol-5P absent from cell (PubMed:30240188). Decreases cellular levels of ribose-5P and ribulose-5P (PubMed:30240188). Decreases cytosolic levels of citrate and oxoglutarate in the presence of hydrogen peroxide (PubMed:20371607). Double knockouts of ZWF1 and YHM2 show an increased mitochondrial NADPH/NADP(+) ratio in the presence of hydrogen peroxide (PubMed:20371607). Reactive oxygen species (ROS) levels are moderately increased following hydrogen peroxide treatment; in double knockouts of YHM2 and ZWF1 there is a larger increase (PubMed:20371607). Present with 15000 molecules/cell in log phase SD medium. Belongs to the glucose-6-phosphate dehydrogenase family.