Stereospecific binding of morphine to phosphatidyl serine

By measuring the adsorption of 14C-morphine to a surface film at an air-water interface, it was shown that morphine binds to phosphatidyl serine in a 1:1 molar ratio. With the use of levorphanol and the inactive d-isomer, dextrorphan, it could be demonstrated that the interaction was stereospecific. A Lineweaver-Burk plot disclosed that levorphanol and morphine competitively interacted with the lipid; the Km for morphine was 1.6 X 10(-5)M and the Ki for levorphanol was 4.8 X 10(-5)M. Heroin, a stronger opiate, had a greater affinity for phosphatidyl serine than did morphine or levorphanol.