IDENTIFICATION OF VITELLOGENIN RECEPTORS IN THE OVARY OF A TELEOST FISH, THE MEDITERRANEAN SEA BASS (DICENTRARCHUS-LABRAX)

The characterization of vitellogenin (VTG) receptors in ovarian membra nes from vitellogenic female sea bass (Dicentrarchus labrax) is descri bed. Incubation of membrane proteins with radiolabeled VTG (I-125-VTG) after SDS-electrophoresis showed specific binding of (125)1-VTG to a protein band of 100 kDa. Filter binding assays showed that binding of I-125-VTG to membrane receptors was saturable with increasing amounts of I-125-VTG. Scatchard analysis of the saturation data revealed a sin gle class of binding sites with an apparent KD Of 1.04.10(-8) M. The s pecificity of the VTG receptors was tested in competition assays; bind ing of I-125-VTG to ovarian membranes was completely abolished with an excess of purified sea bass VTG (cold VTG, VTG degrees) or plasma fro m estradiol (E2)-treated fish, while the addition of control male plas ma (without VTG) caused negligible effect.