Covalent modificaition of juvenile hormone binding proteins by photoaffinity labeling: An unexpected gel shift effect

The 32 kD juvenile hormone binding protein (JHBP) and two 80 kD proteins in larval Manduca sexta hemolymph were labeled with [3H]FDK, a photoaffinity analog of methyl farnesoate (MF). The labeling could be completely displaced by a 30-fold excess of either MF or JH II, demonstrating that [3H]FDK binds specifically to the JH binding sites of the 32 kD JHBP and the 80 kD proteins. In addition, a high molecular-mass protein was labeled with [3H]FDK; labeling could be displaced by excess MF but not by JH II, demonstrating the selectivity in binding MF. The 32 kD JHBP also appeared to weakly bind the potent juvenoid, methoprene, at the JH binding site. Covalent modification by [3H]FDK induced a …