Monoclonal antibody to enkephalins with binding characteristics similar to opiate receptor

Monoclonal antibodies to enkephalins were established by immunization of mice with met-enkephalin, leu-enkephalin or both. Twenty-three clones with a high titer were classified into 6 types according to the binding properties to enkephalins and their derivatives. Antibody LM 239 showed binding characteristics similar to opiate receptor. It has a very high affinity to enkephalins and their derivatives which have a potent opioid activity, but a low affinity to enkephalin derivatives which devoid of opioid activity. The binding of 3H-met-enkephalin to the antibody was inhibited by naloxone and morphine, although the ID50 values were considerably higher than the Ka values of the alkaloids to opiate receptor.