Lectins are carbohydrate-binding proteins. they can, therefore, be purified using affinity chromatography, however, the lectin loses its activity once bound to the carbohydrate of choice in the process. This is because the carbohydrate-binding domain of the lectin is already occupied by the sugar employed in the purification. if the downstream target for the purification required the lectin to have a free carbohydrate-binding domain, there is a need to unbound the lectin from the sugar.