Newly identified organic anion-binding proteins in rat liver cytosol

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) Mr 45 000 containing the glutathione S-transferases, and (b) Mr 35 000 referred to as Y'. Two proteins (Dv and D1) were purified from the Y' fraction. Dv is a basic protein consisting of four subunits of Mr 8000-9000 and selectively binds 1-anilino-8-naphthalene sulfonate and sulfobromophthalein. D1 is a monomer (Mr 40 000) which exhibits high affinity binding for Rose Bengal. Dv protein bound a broad spectrum of organic anions. Antibody raised in rabbits to rat Dv 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.