Microsomal juvenile hormone binding proteins in the follicle cells of Tenebrio molitor

The microsomal fraction of Tenebrio molitor follicle cells has been found to contain both high and low affinity binding sites for juvenile hormone (JH) III. Using Scatchard analysis, the equilibrium dissociation constants, Kd, were calculated as 1.0 x 10(-8) and 4.3 x 10(-7) M respectively. Kinetic data support a rapid binding of the hormone to the site(s), with rate constants of ka = 3.77 x 10(8) M-1 min-1 and kd = 0.0075 min-1. Affinity of the binding site(s) for JH III was higher than for either JH I or methoprene. The significance and possible function of such microsomal binding proteins are discussed, with reference to the perturbance of vitellogenesis found in beetles parasitized by Hymenolepis diminuta.