THE PROTHORACICOTROPIC HORMONE BOMBYXIN HAS SPECIFIC RECEPTORS ON INSECT OVARIAN-CELLS

Bombyxin II, a product of the brain of the adult silkmoth, Bombyx mori , binds to ovarian cells of three different species of lepidoptera, i. e. B. mori (silkmoth), Samia cynthia ricini (ailanthus moth), and an o varian cell line of Spodoptera frugiperda (Sf9) (fall armyworm). Crude Sf9 cell membrane preparations were used to show that the purported b ombyxin receptor binds its ligand in a specific, saturable, and revers ible manner. The dissociation constant of the bombyxin-receptor comple x is 260+/-90 pM. Quantitative binding studies and Scatchard analysis suggest that every Sf9 cell displays 20 000 receptors on the surface. The cross-linked bombyxin-receptor ligand complex has an apparent mole cular mass of about 300 kDa as determined by SDS/PAGE. Reduction cause s the bombyxin receptor to dissociate into two subunits with molecular masses of 90 kDa and 116 kDa. The size and subunit structure of the p utative bombyxin receptor on Sf9 cells show some similarities to the m ammalian insulin receptor.