Differential effects of cyanogen bromide on ligand binding by mu, delta and kappa opioid receptors.

Guinea pig brain membranes treated with cyanogen bromide (CNBr) demonstrate a loss in the number of mu opioid receptors and a lower binding affinity of delta opioid receptors. These receptor changes are irreversible. Results from ligand protection experiments support the hypothesis that the location of the methionine groups, the sites at which CNBr cleaves peptides, differs between these two types of opioid receptors. Kappa receptors are significantly less sensitive to the action of CNBr than mu or delta receptors.