Identification of a large from of the chick liver estrogen receptor

Chick liver cytosol contains an approximately 85 form of the estrogen receptor which can be visualized on sucrose gradients if the cytosol is prepared in the presence of sodium molybdate. This large form of the receptor may also be observed on gel filtration columns where it migrates as a molecule with a Stokes' radius of approximately 6 min. This receptor form can be partially purified and freed from non-specific binding components by chromatography on heparin-Sepharose. One eluted, the receptor has a sedimentation coefficient of 6.2S. The 6.2S form may be further "transformed" to a 5-5.5S receptor once molybdate is removed. The form present in th nucleus of estrogen-treated chicks is 4.5S. These results indicate that the estrogen receptor of chick liver is similar to all other steroid receptor so far described: a large cytoplasmic form of the receptor, which can be stabilized by molybdate, is transformed to a smaller nuclear form. There appear to be small differences in the physical characteristics of the estrogen receptors of chick liver and oviduct.