Catalyzes the oxidative decarboxylation of 6-phosphogluconate to ribulose 5-phosphate and CO(2), with concomitant reduction of NADP to NADPH. 6-phospho-D-gluconate + NADP(+) = CO2 + D-ribulose 5-phosphate + NADPH Carbohydrate degradation; pentose phosphate pathway; D-ribulose 5-phosphate from D-glucose 6-phosphate (oxidative stage): step 3/3. Forms homodimer (PubMed:27366940). Forms heterodimers with PGD1 or PGD2 (PubMed:27366940). Belongs to the 6-phosphogluconate dehydrogenase family.