The use of a juvenile hormone binding protein for the quantitative assay of juvenile hormone

The suitability of the haemolymph juvenile hormone binding protein (JHBP) of Locusta migratoria for use in a competition assay for juvenile hormone (JH) III has been investigated, and a simple quantitative assay procedure using this protein has been developed. JHBP partially purified from haemolymph of precocene treated adult locusts gives rapid and stable binding of [3H]10R-JH III, and can be separated from the unbound hormone with hydroxylapatite (HAP). The sensitivity of the method is such that 0.15 pmol (40 pg) 10R-JH III gives 50% displacement of [3H]10R-JH III from the binding protein. Competition by JH II is about 5 times less and JH I about 10 times less than that by JH III, JH III diol and acid compete at least 1000 times less strongly. A procedure for extraction and assay of JH from 50 microliters haemolymph samples is described, the interference by non-specific haemolymph components is shown to be relatively small, and some data on JH III titres in maturing adult locusts are presented.