High-affinity juvenile hormone binding to fat body cytosolic proteins of the bollworm, Heliothis zea: Characterization and interaction with allelochemicals and xenobiotics

High-affinity saturable binding of juvenile hormone (JH) I was demonstrated in crude fat body cytosol preparations from fifth instar larvae of the bollworm, Heliothis zea (Boddie). Separation of binding proteins from JH metabolizing enzymes was achieved by ammonium sulfate fractionation of cytosolic proteins. Binding kinetics for the 70–100% ammonium sulfate fraction indicated a K d of 4.56 n M and a B max of 1.19 pmol/mg protein. Competition experiments showed similar displacement of [ 3H]JH I from its binding site(s) by JH I and JH III and somewhat less displacement by the synthetic analog, methoprene. The cotton allelochemical myrcene was nearly as competitive as JH I, while its stereoisomer ocimene did not compete at all. The cotton allelochemical gossypol did not compete. The man-made xenobiotic TCDD was a weak competitor. The data establish procedures for JH binding assays in the bollworm and indicate that the same binding protein(s) interacts with insect juvenile hormones, a plant allelochemical, and man-made xenobiotics.