title: Charcoal as a phase separating agent in ligand assays: mechanism of action and the effect of dextran and various proteins on the adsorption of of small molecules.
abstract: In ligand assays, charcoal mixed with dextran is sometimes used to separate free from bound ligand. This is done with the view that dextran "coats" the charcoal and produces a sieve effect on its surface. To further elucidate the mechanism of differential adsorption of small molecules to charcoal, studies were made on the interaction between a number of commonly measured ligands and charcoal, either unmixed or mixed with dextran, albumin, immunoglobulin (IgG) or insulin. "Coating" with dextran was shown not to have any effect on subsequent adsorption of the various ligands. However, coating charcoal with albumin, IgG or insulin did have an effect and even augmented subsequent adsorption of small molecules under certain conditions. It is concluded that the use of "dextran coating" of charcoal to give a sieve effect for the separation of small molecules from large ones is unnecessary and has no basis in fact. This is not the case for coating charcoal with proteins.
mesh_terms: D000818:Animals; D002417:Cattle; D002606:Charcoal / Q000494:pharmacology*; D003911:Dextrans / Q000494:pharmacology*; D007163:Immunosorbent Techniques; D007328:Insulin / Q000378:metabolism; D046911:Macromolecular Substances; D008970:Molecular Weight; D012710:Serum Albumin, Bovine / Q000494:pharmacology; D013997:Time Factors; D014284:Triiodothyronine / Q000378:metabolism
chemical_list: D003911:Dextrans; D007328:Insulin; D046911:Macromolecular Substances; D014284:Triiodothyronine; D002606:Charcoal; D012710:Serum Albumin, Bovine