Identification, Purification, and Partial Characterization of an Organic Anion Binding Protein from Rat Liver Cell Plasma Membrane

Abstract

A B S T R A C T Uptake of bilirubin, sulfobromophthalein (BSP), and other organic anions by the liver is a process with kinetics consistent with carrier mediation. The molecular basis ofthis transport mechanism is unknown. In the search for the putative organic anion carrier or receptor, the interaction of BSP with rat liver cell plasma membrane (LPM) has been studied.

Physicochemical and immunohistological studies of a sulfobromophthalein- and bilirubin-binding protein from rat liver plasma membranes.

“…Further evidence for similarity derives from their identical sialic acid content, the 4 mol/mol of protein dimer reported above corresponding to the 2 mol/mol of 55,000-D subunit reported for OABP (14). Finally, in preliminary experiments, an antibody to OABP cross-reacted with a sample of the intact, 105,000-D BSP/bilirubin-binding protein.…”

“…Despite some evidence of overlapping specificities (5-7), this system is distinct from the principal bile acid transport mechanism (1,8,9). Studies of rat liver plasma membranes (LPM) have demonstrated the specific binding of BSP to a high-affinity binding site (10), and isolation of liver cell membrane proteins with high affinities for BSP and bilirubin has been reported by several groups (11)(12)(13)(14). The present report describes further studies of a BSP-binding membrane protein from rat liver, and the use of a rabbit antibody to this protein to demonstrate both its identity to the bilirubin-binding protein described earlier (13) and its role in the specific binding of BSP and bilirubin to rat LPM.…”

Role of chloride and intracellular pH on the activity of the rat hepatocyte organic anion transporter.

“…Unidirectional pH gradients were formed to determine the effect of cellular pH on initial uptake of 36C1. There was no effect of inwardly or outwardly directed gradients of pH (6)(7)(8) tein; n = 3, P > 0.05). However, initial uptake of "S-BSP with an inwardly directed H' gradient (n = 4) (outwardly directed OH-gradient) was approximately twice that with an outwardly directed H' gradient (n = 4) (inwardly directed OH-gradient) (P < 0.02) (Fig.…”

Hepatic bilirubin uptake in the isolated perfused rat liver is not facilitated by albumin binding.

“…DISCUSSION Bilirubin uptake by the liver is a rapid process of high specificity that has kinetic characteristics which suggest carrier-mediation (3,5). The nature of the carrier is unknown, although several candidates have been identified and purified from rat liver cell plasma membrane preparations (24)(25)(26).…”