BINDING CHARACTERISTICS OF A POTENT ENKEPHALIN ANALOG

A radioiodinated form of the highly potent enkephalin analog FK 33-824 has been characterized with respect to its binding properties in vitro. 125I-FK 33-824 is distinctive among the short opioid peptides in three ways. First, 125I-FK 33-824 binds stereospecifically to rat brain homogenates with very high affinity (Kd = 0.42 nM). Secondly, dissociation of the 125l-labelled peptide from membrane-bound opiate receptors occurs with a relatively long τ 1 2 of 25 min at 4° in contrast to other enkephalins which dissociate more rapidly. Third, competitive binding analyses reveal that the 125l-FK 33-824 binds equally well to both enkephalin (δ) and morphine (μ) classes of opiate receptors. These characteristics distinguish the 125l-labelled peptide as a particularly suitable probe for molecular studies and purification of the opiate receptor. © 1979.