Structural and functional studies of ligandin, a major renal organic anion-binding protein.

Abstract

Sephadex gel filtration of the 100,000 g supernate of homogenates of rat kidney revealed binding of various organic anions (penicillin, Bromsulphalein [BSP], bilirubin, phenolsulfonphthalein [PSP], phlor- izin, glutathione [GSH], p-amino hippurate (PAH), probenecid, conjugated bilirubin, and BSP-GSH) to a nonalbumin-containing protein fraction (Y), which precipitated on addition of monospecific anti-rat liver ligandin (Y protein)-IgG, but not control IgG. Quan- titatively similar organic anion binding was observed in vivo after injection of BSP, BSP-GSH, phlorizin, probenecid, conjugated bilirubin, PAH, or penicillin. The binding protein was purified to apparent homoge- neity and is a basic protein (pI 8.9) of 44,000 daltons with two apparently identical subunits of 22,000 daltons. Monospecific antibody was produced against the renal protein. The results of binding studies in vivo and in vitro and physicochemical, immunologic, structural, and binding site investigations indicate that the renal protein is identical to hepatic ligandin. Immunofluores- cent studies utilizing anti-ligandin IgG previously lo- calized ligandin in the kidney to all proximal tubular cells.