The enzyme that facilitates the transportation of carbon dioxide in red blood cells as bicarbonate ions is carbonic anhydrase.

Here's how it works:

1. Carbon dioxide (CO2) diffuses from the tissues into red blood cells.

2. Carbonic anhydrase catalyzes the reaction between CO2 and water (H2O) to form carbonic acid (H2CO3).

3. Carbonic acid quickly dissociates into bicarbonate ions (HCO3-) and hydrogen ions (H+).

4. Bicarbonate ions diffuse out of the red blood cells into the plasma.

5. Hydrogen ions bind to hemoglobin, preventing a significant change in blood pH.

This process is reversible, allowing the bicarbonate ions to be converted back to CO2 in the lungs for exhalation.