Characterization of juvenile hormone‐binding proteins of hemolymph of Locusta migratoria

The binding of juvenile hormone (JH) by components from hemolymph of adult female Locusta migratoria was characterized to establish whether hemolymph JH-binding proteins could be distinguished from a protein of fat body (BP-1) that may be a JH receptor. Hemolymph was analyzed by the hydroxyapatite assay, gel separation chromatography, polyacrylamide gel electrophoresis, and density gradient centrifugation. Three fractions that bound JH were separated from whole hemolymph by DEAE cellulose column chromatography, and these differed from all three cytosol-binding components. The major hemolymph component (H-A) showed relatively stable binding of JH, a slight loss of binding capacity after delipidation, and a Kd for JH-I of 16 nM. The Kds for JH-l and JH-lll with unfractionated hemolymph were 26 and 42 nM respectively. The order of effectiveness of competitors for binding of [3H]JH-l was JH-lll > JH-l ≫ methoprene > hydroprene ≫ acids of methoprene and hydroprene. The data indicated that unlabeled JH-lll was bound more effectively than its radioactive counterpart. The sedimentation values determined by sucrose density gradient ultracentrifugation were 13-14 S for hemolymph, and the sedimentation value was not altered by the inclusion of 0.4 M KCl throughout the gradient. The data indicated that H-A resembled the specific JH carriers and differed from the putative receptor of fat body cytosol by several criteria.