VISUALIZATION OF THE CHICKEN OOCYTE LIPOPROTEIN RECEPTOR BY LIGAND BLOTTING WITH BIOTINYLATED PLASMA AND YOLK VERY-LOW-DENSITY LIPOPROTEINS

The laying hen 95-kDa oocyte membrane receptor that transports hepatic ally synthesized very low density lipoprotein (VLDL) and vitellogenin (VTG) from the plasma to growing follicles was visualized by ligand bl otting with biotinylated VLDL followed by enhanced chemiluminescence ( ECL) detection. Plasma and egg yolk VLDL were isolated by ultracentrif ugation and free epsilon-amino groups of lysines of apolipoprotein B ( apo B), the protein constituent of VLDL that mediates binding to the 9 5-kDa oocyte membrane receptor, were biotinylated using D-biotin-N-hyd roxysuccinimide ester. An apo B concentration of approximately 223 pM was sufficient to give a signal on 2.5 mug of protein from a chicken o ocyte membrane detergent extract. Western blotting (immunoblotting) of the laying hen 95-kDa receptor with polyclonal rabbit anti-chicken oo cyte VLDL receptor IgG resulted in an ECL signal with the same positio n of migration as that observed in ligand blots using biotinylated pla sma and yolk VLDL. Binding of biotinylated plasma or yolk VLDL to the 95-kDa receptor was abolished by excess unlabeled plasma or yolk VLDL, respectively, as well as by EDTA. Receptor binding activity of biotin ylated plasma and yolk VLDL was also demonstrated by a reverse ligand blotting procedure. Compared with conventional techniques involving th e use of I-125-labeled ligands or antibodies, the laying hen 95-kDa oo cyte membrane lipoprotein receptor can be safely and rapidly visualize d with excellent sensitivity using the present nonradioactive method. In addition, it is suggested that ECL detection can be employed to fur ther study the ligand-binding properties and specificity of this prote in, which is essential to vitellogenesis in the chicken.