Molecular Pharmacology, Vol 12, 494-503, Copyright © 1976 by the American Society for Pharmacology and Experimental Therapeutics

The Purification of an Organic Cation-Specific Binding Protein from Dog Kidney

¹ Department of Pharmacology, State University of New York, Upstate Medical Center, Syracuse, New York 13210

A carrier-mediated mechanism has been postulated for the renal transport of organic cations. An indirect assay, based upon the capacity of an organic cation, N¹-methylnicotinamide, to protect against [¹⁴C]dibenamine alkylation, was used to quantitate the carrier protein during the isolation procedures. Following solubilization from kidney membranes with the nonionic detergent Lubrol WX, the carrier protein was purified to apparent homogeneity as indicated by polyacrylamide gel electrophoresis. The protein has both lipid and carbohydrate associated with it. Sodium dodecyl sulfate (SDS)-gel electrophoresis separated the components, with the bulk of the material appearing as a carbohydrate-lipid-protein complex that migrated faster than the tracking dye. In the SDS-gel experiments [¹⁴C]dibenamine was found to be covalently bound at a narrow locus, and this binding was "protected" by N¹-methylnicotinamide. The data are insufficient to prove that the isolated protein is the carrier for organic cations, but are consistent with this interpretation.