G6PD and lung carcinoma: Glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the pentose phosphate pathway, was found to be modified and activated by O-GlcNAcylation in response to hypoxia, and the level of O-GlcNAcylated G6PD was higher in lung cancers than in matching normal lung tissue [13].