The specificity of antimorphine and antimeperidine antibodies and their reactivity with opioid peptides.

The specificity of antimorphine and antimeperidine antisera was measured by competitive displacement of immunizing radiolabeled haptens. Antimorphine antisera demonstrated a high degree of specificity for a conformation of the phenylpiperidine moiety contained within the structures of morphine and its congeners of the morphinan and benzomorphan series. Antimeperidine antisera demonstrated a high degree of specificity for a different conformation of the phenylpiperidine moiety represented within the structures of meperidine and its semisynthetic derivatives. The reactivity of methionine- and leucine-enkephalin, several synthetic enkephalin analogs, and alpha- and beta-endorphin with the antibodies was tested using purified immunoglobulin G in order to avoid serum-induced proteolysis. No significant cross-reactivity of antimorphine antibodies with any of the opioid peptides was detected. All of the opioid peptides tested exhibited weak but immunologically specific cross-reactivity with antimeperidine antibodies. These findings suggest that conformations analogous to the phenylpiperidine moiety in morphine as have been proposed for [Tyr1] in opioid peptides do not appear to be present as measured by immunochemical methods. A conformation with weak stereochemical similarity to the phenylpeperidine moiety in meperidine does appear to be present. The possible homologies between [Phe4] of opioid peptides, meperidine and hydrophobic side chains of certain oripavine derivatives are discussed.