The binding of cholic acid to protein in rat serum and liver.

After the intraperitoneal administration of radioactive cholic acid to rats, the binding of the cholic acid to protein was immunologically investigated. The serum and liver cytosol were separately incubated with antiligandin or antialbumin immunoglobulin and then subjected to sucrose density gradient centrifugation. The sedimentation behavior of the radioactivity, endogenous bile acids, glutathione S-transferase activity of ligandin and protein provided evidence that cholic acid is bound to both ligandin and albumin in liver, and mostly to albumin in serum. However, little, if any, cholic acid seems to be bound to protein in bile. These results suggest that ligandin and albumin are the major physiological carriers of bile acid.