[Biocytin¹³]Dynorphin A 1-13 Amide: A Potential Probe for the κ-Opioid Receptor

A dynorphin A 1-13 amide (DYN) derivative biotinylated in position lysine 13 (B-DYN) has been prepared by automated solid-phase peptide synthesis. The derivative retained its ability to bind to avidin, and B-DYN–avidin complex showed a dissociated half-life of 10 hr at 37°C. Opioid receptor binding was measured in membrane preparations of rat brain (µ), NG-108-15 neuroblastoma–glioma hybrid cells (δ), and guinea pig cerebellum (κ). Biotinyl substitution of DYN either did not affect receptor binding (δ) or slightly reduced binding affinity (µ and κ). Binding of B-DYN to the κ receptor was very tight, with an IC₅₀ value in the low picomolar range, while binding to µ and δ sites was over two orders of magnitude lower. Preassociation of B-DYN with avidin resulted in a reduction of the affinities to the investigated opioid receptors by 100- to 1000-fold. However, the apparent affinity of B-DYN–avidin for the κ-opioid receptor is sufficient to suggest that B-DYN may be a useful tool for κ-opioid receptor assay, localization, and purification.