ISOLATION OF AN ORGANIC ANION BINDING-PROTEIN FROM RAT-LIVER PLASMA-MEMBRANE FRACTIONS BY AFFINITY CHROMATOGRAPHY

As part of a study of hepatic organic anion transport, solubilized liver plasma membrane proteins were subjected to affinity chromatography on bilirubin- and sulfobromophthalein-labeled agarose columns. Both columns retained a Sudan Black and PAS negative protein of molecular weight 60,000 daltons, which cochromatographed with [35S]sulfobromophthalein on Sephadex G-75, and reversibly bound [35S]sulfobromophthalein in vitro with high affinity (Ka {reversed tilde equals} 107 M-1) and a valence of 2. Erythrocyte ghost membranes did not contain this protein. Sulfobromophthalein-agarose retained two additional smaller proteins which did not cochromatograph with [35S]sulfobromophthalein. Their significance is unclear. This study supports the hypothesis that liver cell plasma membranes participate in the hepatic transport of organic anions. © 1979.