Characterization of proctolin binding sites on locust oviduct membranes

Abstract

The binding of [ 3H]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 μM and a B max of 96.3 ± 16.7 pmo/mg protein. Binding was specific in thatcompetition experiments with a wide range of peptides showed that only Arg-Tyr-Leu-Pro-Ala was an effective competitor at μM concentrations. All other peptides examined weekly reduced proctolin binding at concentrations above 50 μM. Certain peptides were found to potentiate [ 3]pproctolin binding at low μM concentrations (1–10 μM) and to inhibit proctolin binding at higher concentrations. The significance of these findings is discussed.