“Unboun” ligand dsorption on dextran-coated charcoal: Practical consideration

Abstract

Some practical aspects of estrogen binding to Dextran-coated charcoal were studied. The binding capacity of the charcoal was very large and not limitative in most instances. The affinity depended on its degree of dispersion in the medium. At 40 mg% of charcoal less than 2% of free [ 3H]estradiol ( 3H-E 2) remained in the supernatant. At high concentrations (more than 200 mg%), charcoal was able to precipitate most of the BSA bound 3H-E 2, but none of the 3H-E 2 bound to rat uterus cytosol prepared in Tris-EDTA buffer. BSA added to rat uterus cytosol decreased the amount of 3H-E 2 not precipitated with charcoal. Charcoal was able to remove 3H-E 2 or 3H-E 2 from some specific antibodies, but not from others. Time and temperature of incubation in the presence of charcoal were critical in this respect. Precipitated charcoal was still able to adsorb the estrogen moiety, slowly released from the antibody in function of time. Practical considerations are discussed concerning the use of dextran-coated charcoal in radioimmunoassay procedures.