Figure 3. Role of AE1 in the uptake of CO₂ erythrocytes in systemic capillaries.

CA II is carbonic anhydrase II, a soluble enzyme that also can bind to the C terminus of AE1. Hb is hemoglobin, Hb-O₂ is hemoglobin fully saturated with four O₂ molecules, and Hb–H⁺ is protonated hemoglobin that binds three O₂ molecules. CO₂ may, in part, enter the cell via the water channel AQP1. In the pulmonary capillaries, all of the reactions reverse, releasing CO₂ into the blood plasma.