Juvenile hormone-binding protein from the cytosol of Drosophila Kc cells

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Abstract
Insect cells of an established line, Drosophila Kc cells, take up and metabolize juvenile hormone (JH). The cytoplasm of these cells contains a protein that binds JH with specificity, saturability, and high affinity ( K d = 1.56 × 10 -8 M). The kinetics for the specific binding and dissociation of JH I were independently measured, and the rate constants were found to be k a = 1.3 × 10 6 M -1 min -1 , k d = 1.3 × 10 -2 min -1 , respectively. All three juvenile hormones bind to the protein with comparable affinities; the corresponding acid or diol metabolites of JH I are not bound. About 2500 hormone-binding protein molecules are present per cell. The protein has a molecular weight of 80,000 as estimated by gel permeation chromatography and by sucrose gradient sedimentation. The properties of this protein suggest that it functions as a cytoplasmic receptor for juvenile hormone.