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

Abstract

Insect cells of an established line, D. melanogaster 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 (Kd = 1.56 .times. 10-8 M). The kinetics for the specific binding and dissociation of JH I were independently measured, and the rate constants were Ka = 1.3 .times. 106 M-1 min-1, Kd = 1.3 .times. 10-2 min-1, respectively. All 3 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/cell. The protein has a MW 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 JH.