Pathways of energy metabolism in the erythrocyte. Glucose 6-phosphate may be degraded anaerobically to lactate through the Embden–Meyerhof pathway, or oxidatively through the hexose monophosphate shunt. Pentose phosphates (R-5-P) can reenter anaerobic glycolysis as fructose 6-phosphate (F-6-P) and glyceraldehyde 3-phosphate (G-3-P) after conversion by enzymes of the terminal pentose phosphate pathway or as a product of adenosine or inosine degradation. 2,3-diphosphoglycerate (2,3-DPG) may be generated instead of adenosine triphosphate (ATP) through diversion of triose through the Rapoport–Luebering shunt. Glutathione may be synthesized directly from constituent amino acids; its cycling from oxidized (GSSG) to reduced forms (GSH) depends on reduced pyridine cofactor (NADPH) generation. ADP indicates adenosine diphosphate; DHAP, dihydroxyacetone phosphate; FDP, fructose 1,6-diphosphate; NAD, nicotinamide adenine dinucleotide; NADP, nicotinamide adenine dinucleotide phosphate; NADPH, nicotinamide adenine dinucleotide phosphate, reduced form; and PEP, polyestradiol phosphate. Reproduced with permission from Gallagher.⁴²