Juvenile hormone binding by components of fat body cytosol from vitellogenic locusts

Binding of 3H-labeled juvenile hormone (JH) to cytosol components of fat body from adult female Locusta migratoria, a tissue in which JH stimulates vitellogenin synthesis, has been characterized. Protein-bound JH is separated from unbound hormone with hydroxyapatite, which is found to provide a more sensitive and less variable assay than use of dextran-coated charcoal. By chromatography on DEAE-cellulose, three JH-binding components have been separated from cytosol. BP-I exhibited relatively stable binding with little degradation of the hormone, gave a Kd for JH-I by Scatchard analysis of 1.69 X 10(-8) M, and binding of JH-I was competed by JH-I and several synthetic JH analogs in an order corresponding to their JH activities. These characteristics suggest that BP-I may be a cytoplasmic JH receptor. BP-II, a minor component, also bound JH-I stably, but competition by analogs was not correlated with their hormone activity. BP-III caused rapid degradation of JH to JH acid and may be an esterase.