Nature of progesterone action on amino acid uptake by isolated full-grown oocyte of Xenopus laevis

l-leucine uptake into full-grown oocytes of Xenopus laevis is a saturable process which is Na⁺ dependent and presumably coupled to Na⁺ gradient. Our results indicate that progesterone (10^?6 M) blocks abruptly, around the germinal vesicle breakdown, the saturable transport of l-leucine. $\text{p-}\text{Chloromercuribenzoate}$ (10^?4 M) induces maturation and after a short lag of time strongly inhibits l-leucine uptake. Cycloheximide prevents progesterone-induced maturation and permeability changes.