Cytosolic and nuclear juvenile hormone-binding proteins from the brain of Diploptera punctata

Cytosol and crude nuclear extracts of brains from female Diploptera punctata were found to contain a juvenile hormone-binding protein. The binding kinetics of the cytosol and nuclear juvenile hormone-binding proteins toward racemic [3H]JH III were determined using the dextran-coated charcoal assay. Both proteins show reversible and saturable binding toward JH III. The mean dissociation constant (Kd) of the brain cytosol binding protein was 66.5 +/- 7.2 nM, whereas the nuclear-binding protein had a lower affinity, with a mean Kd of 170 +/- 22.1 nM. The specificity of both the cytosol and the nuclear binding proteins was determined by competitive displacement experiments with [3H]JH III. For the cytosol binding protein, the order of relative affinity was JH II > (10R)-JH III > (10RS)-JH III approximately JH I. For the nuclear binding protein the order of relative affinity was JH II > JH I > (10R)-JH III > (10RS)-JH III. The JH analog hydroprene (ZR 512) had > 100-fold lower affinity than JH III for both proteins.