The progesterone receptor‐like properies of Xenopus laevis oocyte melanosomes are probably due to eumelanin

The binding of progesterone to the melanosomes of the Xenopus laevis oocyte was examined. Based upon the similarities between the eumelanin complex, which is prepared by stripping melanosomes of their proteins, and synthetic melanin in regard to their association with progesterone and other steroids, the data strongly suggest that eumelanin rather than a protein is responsible for the receptor‐like properties of the melanosomes.