Binding of the endogenous nonpeptide morphine-like compound to opiate receptors

The endogenous central nervous tissue substance called MLC (morphine-like compound) is shown to bind to the opiate receptors of the mouse neuroblastoma X glioma hybrid cell line NG108-15. The interaction of MLC with these opiate receptors is noncooperative, as is the interaction of morphine, naloxone, and Leu-enkephalin with these receptors. A specific antibody to morphine will bind MLC but will not bind beta-endorphin, Leu-enkephalin, or Met-enkephalin. It would appear, therefore, that MLC can be considered to be a different type of endogenous ligand for the opiate receptor.