transporter binding bile transporter substrate bile trans substrate PSI-MI MI:2129 The prediction of the value for this paramater is currently not possible. Substrate of the bile acid carrier system in both the intestinal tract and the liver. System catalyses of the transfer of bile acid from one side of the membrane to the other. Bile acids are any of a group of steroid carboxylic acids occurring in bile, where they are present as the sodium salts of their amides with glycine or taurine.