CHARACTERIZATION OF PROCTOLIN BINDING-SITES ON LOCUST OVIDUCT MEMBRANES

The binding of [H-3]proctolin to oviduct membranes has been analyzed to investigate the nature of proctolin binding sites in the oviduct. Proctolin binding was found to be time dependent, proportional to concentration of membrane protein, saturable, specific and reversible. Two apparent proctolin binding sites were recognized. The first had a K(d) of 400 +/- 82 nM and a B(max) of 23.7 +/- 6.7 pmol/mg protein. The second had a K(d) of 2.4 +/- 0.2 muM and a B(max) of 96.3 +/- 16.7 pmol/mg protein. Binding was specific in that competition experiments with a wide range of peptides showed that only Arg-Tyr-Leu-Pro-Ala was an effective competitor at muM concentrations. All other peptides examined weekly reduced proctolin binding at concentrations above 50 muM. Certain peptides were found to potentiate [H-3]proctolin binding at low muM concentrations (1-10 muM) and to inhibit proctolin binding at higher concentrations. The significance of these findings is discussed.