The molecular switch regulating oxygen-dependent red cell properties. (A) Oxygenated Hb has a lower affinity for band 3, so that glycolytic enzymes and ankyrin remain strongly bound and the ATP release channel is closed. (B) On deoxygenation, Hb has a higher affinity for band 3, displacing glycolytic enzymes and ankyrin and opening the ATP release channel. Glycolysis is stimulated, the cytoskeleton weakens, and ATP is released. The conformational change of Hb on transition from oxygenated to deoxygenated states, via reversible band 3 binding, therefore represents the molecular switch regulating red cell properties. Figure provided by Haiyan Chu and Philip S. Low.