Structure of chick progesterone receptors.

Oviduct progesterone receptors have been purified from both immature chicks and laying hens. The subunits, progestophilins A and B, have different molecular weights, but each is the same from either tissue source. Immunological data show that the subunits are cross-reactive. The hen B protein as isolated to homogeneity contains nonradioactive progesterone in stoichiometric amounts as shown by gas chromatography-mass spectrometry. These studies further confirm our earlier determinations on these proteins.