We have found that N1-methylnicotinamide (NMN) and p-Aminohippurate (PAH) transport can be reconstituted in phospholipid vesicles by insertion of the solubilized microsomal membranes proteins back into artificial lipid membranes. After solubilization of the plasma membranes with the non-ionic detergent Lubrol WX, the protein solution was added to a phospholipid solution (prepared by dissolving the phospholipid in the detergent) and allowing the phospholipid:protein vesicles to form by dialysis. Our studies show that the transport is dependent on: time; pH; temperature; and protein concentration. In addition, transport is saturable and can be inhibited by known competitors of these transport systems. It appears as if specific phospholipids are required in that only sphingomyelin and phosphatidyl choline will function in reconstituting transport. Using reconstitution as the mode of assaying the proteins throughout an isolation procedure, we achieved a 45 fold purification of the NMN and PAH transport proteins. Interestingly, the two copurify, however, our data clearly show that the two transport systems are distinct entities. BIBLIOGRAPHIC REFERENCES: Holohan, P.D., Pessah, N.L., and Ross, C.R.: The Purification of an Organic Cation-specific Binding Protein from Dog Kidney (1976) Mol. Pharmacol., 12, 494-503.