Now, once inside the blood plasma, the CO2, about 5% of that CO2 remains inside the blood plasma. But the rest essentially enters or diffuses across the membrane of the red blood cells. Now, once inside the red blood cells, what happens is a catalytic enzyme known as carbonic anhydrates, catalyzes the combination of gaseous, CO2 and liquid water to basically form an acid known as carbonic acid. Now, carbonic acid, H two CO2, is a weak acid and that means it will dissociate into bicarbonate, the conjugate base to this acid, as well as a hydrogen ion. Now, this hydrogen ion ultimately leads to the bore effect. It binds onto a special allosteric site on our hemoglobin and that causes the hemoglobin to decrease its affinity for oxygen.