Vitellogenin receptors during vitellogenesis in the rainbow trout Oncorhynchus mykiss.

Rainbow trout vitellogenin receptors have been characterized by ligand blotting and Scatchard analysis. Their evolution has been studied over a reproductive cycle in a broodstock of 2-year-old females. The receptors were prepared from ovarian membrane homogenates and were solubilized using n-octyl-beta-D-glucopyranoside. The visualization of the receptor by ligand blotting using 125iodine-vitellogenin after sodium dodecyl sulfate electrophoresis revealed the existence of one major binding component corresponding to a protein of 113 kDa. The Scatchard transformation of the binding data revealed a single class of binding sites with an apparent Kd of 1.8 x 10(-8) M/L. The variations of the binding characteristics (Kd and maximum binding) were investigated during vitellogenesis. This study revealed that the Kd was not affected by oocyte growth during vitellogenesis, but was highly decreased in ovulated eggs. The receptor number increased during the same period from 35 to 860 fM per oocyte, while the receptor number per mm2 of oocyte membrane surface was doubled during the same period.