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Use of Dextran-Coated Charcoal to Separate Antibody-Bound from Free Hormone: A Critique

Division of Endocrinology and Metabolism, UCLA School of Medicine, Harbor General Hospital Campus Torrance, California

The charcoal adsorption of ¹²⁵IHTSH and ¹²⁵I-HTSH-antibody complex was studied at low and high protein concentrations with uncoated charcoal and charcoal coated with D10, D40, or D150 dextran in varying charcoal concentrations. Both bound and free hormone adsorbed to charcoal, but the adsorption of the "bound" was low compared with that of the "free." Regardless of the protein concentration, the uncoated charcoal was able to carry out an efficient "bound" and "free" separation. However, at low protein concentrations, dextran coating improved slightly the quality of the separation. When high protein concentrations (serum) were present, uncoated charcoal most efficiently separated bound from free hormone. These data indicated that, using the charcoal adsorption phenomenon, proteins are competitive with the hormone and the hormone-antibody complex; adsorption decreases as the protein concentration increases. Dextran coating diminishes, without inhibiting, the complex adsorption and also reduces free hormone adsorption; thus, it is of little or no assistance. Dextran does not act as a "molecular sieve" but acts by reducing the number of free sites for adsorption of both bound and free hormone.

Received May 12, 1972.