Lipophorin: A hemolymph juvenile hormone binding protein in the german cockroach, Blattella germanica

We examined the binding of [ 3H](10 R) juvenile hormone (JH) III to lipophorin that was purified from the hemolymph of Blattella germanica. Binding was found to be specific, saturable and with high affinity to JH III. Using Scatchard analysis, the equilibrium dissociation constant (K d) and total binding capacity (B max) were estimated to be 9.75±0.64 nM and 0.241±0.02 nmol/mg protein, respectively. Competitive displacement studies with racemic JH III, JH I, cuticular hydrocarbon, contact sex pheromone, and the JH analogs pyriproxyfen, fenoxycarb, and hydroprene showed that only JH III readily displaced [ 3H](10 R)JH III from the binding site. However, hydroprene competed for the JH III binding site more effectively than the other two JH analogs. Photoaffinity labelling using the JH III analog [ 3H]epoxyfarnesyl diazoacetate demonstrated that the JH binding site was on apolipophorin-I, the large subunit of the lipophorin complex.