The Presence of a Progesterone Binding Protein in Spermathecae of the Migratory Locust,Locusta migratoria migratorioidesR. & F.

Summary Radioreceptor assays revealed the presence of a progesterone binding protein in the cytosol of spermathecae of the migratory locust, Locusta migratoria migratorioides. The spermathecae were excised from adult females, 1 to 7 days after the final moult. The progesterone binding was characterized by a dissociation constant of 4.6 × 10−8M and a capacity of 0.9 pmoles per milligram protein. Competitive inhibition experiments with other steroids demonstrated the high specificity of the binder for progesterone. Binding disappears in the presence of the proteinase Pronase P, suggesting that the binding factor is a protein.