Newly identified organic anion-binding proteins in rat liver cytosol

Abstract

Previously, all organic anion binding activity in the Y protein (ligandin-containing) fraction of rat liver cytosol has been attributed to the glutathione S-transferases. Gel filtration on Sephadex G-75 superfine has resolved the Y protein fraction into organic anion-binding fractions of two distinct molecular weights: (a) M r 45 000 containing the glutathione S-transferases, and (b) M r 35 000 referred to as Y′. Two proteins (D v and D 1) were purified from the Y′ fraction. D v is a basic protein consisting of four subunits of M r 8000–9000 and selectively binds 1-anilino-8-naphthalene sulfonate and sulfobromophthalein. D 1 is a monomer ( M r 40 000) which exhibits high affinity binding for Rose Bengal. D v protein bound a broad spectrum of organic anions. Antibody raised in rabbits to rat D v showed no cross-reactivity with purified glutathione S-transferases A, B, or C. Thus, we have identified organic anion-binding proteins which are unrelated to the glutathione S-transferases, but which were previously associated with the crude Y-fraction. The relative abundance of these proteins and their binding characteristics suggest their role in hepatic organic anion transport.