Lipid requirement for mu opioid receptor binding.

We have previously shown that a partially purified mu opioid receptor from bovine brain requires lipids to exhibit full binding activity. In the present report, we have determined the specificity of this lipid requirement. Lipids active in this regard were found always to contain an acidic head group and a fatty acid with two or more double bonds. Free, polyunsaturated fatty acids were also able to confer high binding activity on the partially purified opioid receptor. The possible roles lipids play in opioid binding are discussed in light of these data.