CHARACTERIZATION OF A VITELLOGENIN RECEPTOR IN WHITE PERCH (MORONE AMERICANA)

Receptors for white perch vitellogenin (wVTG) were characterized using wVTG, labeled in vivo with [H-3]leucine or in vitro with I-125, and s emipurified ovarian membranes. Specific binding of wVTG to the membran es was temperature-dependent, proportional to the amount of membrane, and saturable. Scatchard analyses revealed a single class of binding s ites of low maximum binding capacity (MBC; similar to 35 pmol VTG/mg m embrane protein) and high affinity (K-d similar to 400 nM), consistent with wVTG levels (540-2700 nM) circulating in maturing females. Ligan d blotting revealed a receptor protein of M(r) similar to 157 000 and a smaller protein, possibly its degradation product. Striped bass vite llogenin, chicken egg yolk very low density lipoprotein, and suramin d isplaced wVTG from its receptor, but BSA did not. No change in K-d was noted over the course of vitellogenesis in maturing perch, and MBC in creased only slightly very late in the gametogenic cycle. The wVTG bou nd specifically to membranes prepared from liver, muscle, and mesenter ic fat, but not to erythrocyte membranes. The K-d for ovary (394 nM) a nd liver (345 nM) were similar, but the K-d for muscle (1440 nM) was m uch higher.