The molecular size of multiple opiate receptors.

The functional size of different types of opiate receptors was determined in situ by the radiation inactivation technique. The Mr of opiate binding sites was estimated to be about 90,000 daltons; the data revealed no significant differences between the molecular sizes of either mu-, delta- or kappa-sites in rat brain membranes. An identical molecular size was found also for the delta-sites in the neuroblastoma X glioma hybrid cell clone, NG 108-15.