Solubilization and characterization of active opiate binding sites from mammalian brain

Active binding sites have been solubilized from cell membranes derived from mammalian brain. High affinity, stereospecific binding to soluble sites was demonstrable when membranes from rat brain, human frontal cortex and bovine corpus striatum were treated with digitonin or glycodeoxycholate, provided that the binding assay was conducted at 25 degrees C or below and in the presence of 50 to 100 mM NaCl. The yield of solubilized binding sites extracted from brain cell membranes was increased substantially (up to 43% yield from bovine striatum) when membranes were treated with detergent solutions containing 0.5 to 1.0 M NaCl. This effect was not observed when LiCl, KCl or (NH4)2SO4 were substituted for NaCl. Evidence for the solubility of the binding sites was provided by two criteria: nonsedimentation after 2 hr of centrifugation at 10(5) X g and an apparent molecular weight of 3 to 4 X 10(5) as determined by gel filtration.