MOLECULAR PHARMAcoLoGY, 33:170-177 Comparison of [1251] 3-Endorphin Binding to Rat Brain and NG1 08-1 5 Cells Using a Monoclonal Antibody Directed Against the Opioid Receptor

The properties of [12511f3h-endorphin-binding sites from rat brain membranes and membranes from the NG1O8-1 5 cell line were compared using a monoclonal antibody directed against the opioid receptor and opioid peptides as probes. The binding of [1251] 3h-endorphin to both rat brain and NG1 08-1 5 membranes yielded linear Scatchard plots with Kd values of 1.2 n and 1.5 nM, respectively, and B values of 865 fmol/mg rat brain membrane protein and 1 077 fmol/mg NG1 08-1 5 membrane pro-tein. A monoclonal antibody, OR-689.2.4, capable of inhibiting and #{246}binding but not K binding to rat brain membranes, noncom-petitively inhibited the binding of 1 nri [1251]flh-endorphin to rat brain and NG1 08-1 5 membranes with an lC value of 405 nM for rat brain membranes and 543 flM for NG1 08-1 5 membranes. The monoclonal antibody also inhibited the binding of 3 n [3H] [D-penicillamine2, D-penicillamine5] enkephalin to NG1 08-1