Equilibrium-dialysis studies of the interaction between cholic acid and 100000g-supernatant preparations from the rat liver

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Abstract
The binding of cholic acid to 100,000 g supernatants from rat livers was investigated by equilibrium dialysis and gel-exclusion chromatography. Supernatants contained at least 2 classes of binding site for cholic acid. These receptor molecules are probably proteins, since incubation with proteolytic enzymes resulted in complete loss of cholic acid binding. Supernatants were added to columns of Sephadex G-75, and 2 groups of fractions were shown to bind cholic acid. One of these contained low-affinity binding sites and the other contained both low- and high-affinity binding sites. Feeding cholestyramine had no effect on cholic acid binding. Increased cholic acid binding occurred after injection of phenobarbitone. There was an increase in the amount of the low-affinity component but no change in the high-affinity component. The dissociation constants of the binding of cholic acid suggest that the binding proteins may be involved in bile acid transport.