IDENTIFICATION OF A SPECIFIC, HIGH-AFFINITY IMIPRAMINE-BINDING PROTEIN FROM HUMAN AND RAT PLATELET MEMBRANES

A specific, [H-3]-imipramine-binding protein (IBP) of high affinity ha s been identified in human and rat platelets. This binding protein was isolated in active form using digitonin as solubilizing agent in pres ence of suitable protease inhibitors (leupeptin, PMSF, and EGTA). Digi tonin effectively solubilized 60-70% and 55-60% of IBP from human and rat platelet membranes respectively. Displacement of [H-3]-imipramine with pharmacological agents was similar in membrane bound and solubili zed receptor. The solubilized receptor retained specific imipramine-bi nding activity after blotting on nitrocellulose. Electrophoretic runs of solubilisate after transfer to nitrocellulose exhibited specific, h igh affinity binding to a bared in the 98 K dalton area. The approach used for the identification of the IBP in this study is not only rapid and convenient but is also highly specific and could be used for iden tification of other receptor proteins for their preliminary characteri zation.