Visualization of progesterone binding to plasma membrane ofxenopusoocytes

Abstract

We have previously shown that oocyte maturation is induced by an immobilized progesterone, progesterone‐3‐carboxymethyloxime ‐ bovine serum albumin conjugate (P‐BSA) in Rana dybowskii. In this study, we confirmed the maturation inducing activity of P‐BSA on Xenopus oocyte and examined the binding character of the immobilized progesterone on the surface of Xenopus oocytes after removal of the vitelline layer. P‐BSA induced maturation of Xenopus oocytes but E‐BSA failed to do so as observed in Rana. Binding of the immobilized progesterone, fluorescein isothiocyanate‐labeled progesterone‐3‐O‐carboxymethyloxime‐BSA (P‐BSA‐FITC) on the devitellined oocytes surface was examined by fluorescence confocal microscopy. The binding affinity of P‐BSA‐FITC to the devitellined oocyte was higher than that of estrogen‐BSA‐FITC (E‐BSA‐FITQ or testo‐sterone‐BSA‐FITC (T‐BSA‐FITC). The binding disappeared in the presence of excess free progesterone but not in the presence of free estrogen. Maximum binding occurred after two‐h...