Mu-opioid receptor is associated with phosphatase activity.

A preparation of purified mu opioid receptor from bovine brain hydrolyzes p-nitrophenylphosphate. This phosphatase activity has a pH optimum of 9.0, a Km of 9.0 microM, and is stimulated by Mn++ and Mg++ ions. Evidence that the observed activity is not due to a contaminant in the opioid receptor preparation includes 1) the activity is associated primarily with 60,000 molecular weight material which is much smaller than bovine brain alkaline phosphatase; and 2) the activity could not be absorbed by antibodies specific for bovine alkaline phosphatase. Thus this appears to be the first demonstration of enzymatic activity associated with an opioid receptor.