Specificity of the juvenile hormone binding protein: The geometrical isomers of juvenile hormone I

Abstract

The binding of the geometrical isomers (>/=99% pure) of juvenile hormone I to the hemolymph juvenile hormone binding protein of Manduca sexta (Lepidoptera, Sphingidae) was analyzed. A technique is described for isomer separation by micropreparative high-resolution liquid chromatography. Analysis of competition was performed by using a "batch adsorption" hydroxylapatite binding assay. Competition studies indicate that the naturally occurring isomer, 2E,6E,10cis, is bound with the highest affinity. Optimal binding appears to depend most heavily upon the configuration of the 2,3 double bond. Juvenile hormone binding protein shows a higher affinity for the 2E than for the 2Z configuration. The 6,7 double bond is of less importance in determining binding activity, and isomerism about the epoxide appears least important in conferring binding activity. The binding site may be a groove along the surface of the binding protein interacting with the side chains of juvenile hormone, including the ester methyl group. The grouping of the side chains and the ester methyl group thus constitutes a distinct hydrophobic face, and the hydrophobic interactions are essential in maintenance of the bound ligand.