G6PD and cancer: Interestingly, while hypoxia causes downregulation of the rate limiting enzyme of the PPP Glucose-6-phosphate dehydrogenase (G6PD) in several cancers (133), glycosylation promotes G6PD activity and increases glucose flux through the PPP, providing precursors for nucleotide and lipid biosynthesis, and reducing equivalents for antioxidant defense.