Bifunctional enzyme which catalyzes the first two steps 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. 6-phospho-D-glucono-1,5-lactone + H2O = 6-phospho-D-gluconate + H(+) D-glucose 6-phosphate + NADP(+) = 6-phospho-D-glucono-1,5-lactone + H(+) + NADPH G6PD activity is inhibited by glucosamine-6-phosphate, NADPH, and 4-(4-bromophenyl)-7-(3,4-dimethoxyphenyl)-4,6,7,8-tetrahydroquinoline-2,5(1 H,3H)-dione. G6PD and 6PGL activities can be reversibly inhibited by S-glutathionylation (in vitro). Optimum pH is 8.0 for G6PD activity. Carbohydrate degradation; pentose phosphate pathway; D-ribulose 5-phosphate from D-glucose 6-phosphate (oxidative stage): step 1/3. Carbohydrate degradation; pentose phosphate pathway; D-ribulose 5-phosphate from D-glucose 6-phosphate (oxidative stage): step 2/3. Homotetramer. In the N-terminal section; belongs to the glucosamine/galactosamine-6-phosphate isomerase family. 6-phosphogluconolactonase subfamily. In the C-terminal section; belongs to the glucose-6-phosphate dehydrogenase family.