Solubilization in good yield of active opiate binding sites from mammalian brain

Active opiate binding sites have been solubilized from mammalian brain cell membranes. The presence of 0.5-0.1 M NaCl during treatment of membranes from rat brain, human frontal cortex, and bovine corpus striatum with glycodeoxycholate or digitonin resulted in the extraction of active opiate binding sites in yields ranging up to 43%. The criteria for solubility of the sites were their inability to sediment at 10(5) x g after 2 hr and their apparent molecular weight of 3- 4 x 10(5) as determined by gel filtration. The receptors in solution resemble the membrane-bound sites with respect to saturability, stereo-specificity, sensitivity to heat and reagents, and high affinity for opioid ligands. The interaction of solubilized sites with immobilized lectins was used to demonstrate the glycoprotein nature of the opiate receptor. Soluble receptors from all species studied were retained by wheat germ agglutinin(WGA)-agarose and could be specifically eluted with N-acetylglucosamine. No retention of solubilized material was observed with eight other lectins examined, including horseshoe crab lectin, a sialic acid specific agglutinin. The receptor protein eluted from WGA columns was enriched 25-50-fold over the crude soluble fraction.