Biological activity of mu opioid receptor

The purification of the mu-opioid receptor has proved to be more difficult than most other receptors for at least two reasons. First, they are easily inactivated by most detergents and the second problem is the heterogeneous existence of the opioid receptor. Despite these problems, this laboratory, and several others, have recently reported purification of the mu-opioid receptor. The 58,000 molecular weight of the purified mu-opioid receptor agrees closely with the value reported by other investigators. In addition, it was found that this purified mu-opioid receptor was associated with a phosphatase activity. While the relevance of this phosphatase activity to opioid receptor action remains to be determined, it is interesting to note that this activity was stimulated by Mn++ and Mg+ ions, both of which also increase opioid binding.