16. Role of Phosphatidyl Serine in the Opiate Receptor*

The molecular nature and configuration of the opiate receptor is a problem under intensive investigation in a number of laboratories (1,2,3). Our interest in the problem developed as a result of a finding of others (4) that a proteolipid fraction from brain may be responsible for stereospecific opiate binding observed in various preparations of brain tissue. Upon examining various lipids, proteolipids, and proteins from membranes derived from brain, it was found that phosphatidyl serine (PS),t the major acidic lipid in brain, exhibited stereospecific opiate binding (5). Since the Kd's for the opiate-PS complex and the opiate-tissue complex differed by three orders of magnitude, it was recognized that the binding to PS was nonspecific and different from the high affinity binding to membrane preparations. What interested us was the possibility that PS, in the form of a complex with a membranous protein, may be an important component of the opiate receptor.