Binding of bile acids by glutathione S-transferases from rat liver.

Binding of bile acids and their sulfates and glucuronides by purified GSH S-transferases from rat liver was studied by 1-anilino-8-naphthalenesulfonate fluorescence inhibition, flow dialysis, and equilibrium dialysis. In addition, corticosterone and sulfobromophthalein (BSP) binding were studied by equilibrium and flow dialysis. Transferases YaYa and YaYc had comparable affinity for lithocholic (Kd approximately 0.2 microM), glycochenodeoxycholic (Kd approximately to 60 microM), and cholic acid (Kd approximately equal 60 microM), and BSP (Kd approximately 0.09 microM). YaYc had one and YaYa had two high affinity binding sites for these ligands. Transferases containing the Yb subunit had two binding sites for these bile acids, although binding affinity for lithocholic acid (Kd approximately 4 microM) was lower than that of transferases with Ya subunit, and binding affinities for the other bile acids were comparable to the Ya family. Sulfated bile acids were bound with higher affinity and glucuronidated bile acids with lower affinity by YaYa and YaYc than the respective parent bile acids. In the presence of GSH, binding of lithocholate by YaYc was unchanged and binding by YbYb' was inhibited. Conversely, GSH inhibited the binding of cholic acid by YaYc but had less effect on binding by YbYb'. Cholic acid did not inhibit the binding of lithocholic acid by YaYa.