• Hb is a buffer (Hb/Hb-H+) in the erythrocytes
• Hb is a carrier of O2 and CO2
Binding of O2 is a cooperative. Hb binds O2 weakly at low oxygen pressures and tightly at high pressures. The binding of the first O2 to Hb enhances the binding futher O2 molecules → allosteric effect → S-shaped (sigmoidal) saturation curve of Hb