A COMPARISON OF THE CYTOPLASMIC ESTROGEN RECEPTORS OF MAMMARY GLAND FROM VIRGIN AND LACTATING MICE1

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Abstract
Recent studies suggest that the mammary cytoplasmic estrogen receptor of virgin mice sediment predominantly as 4S species on low ionic strength sucrose gradients. In the present studies we show that the mammary cytoplasmic estrogen receptor from both the intact and ovariectomized virgin and lactating mice sediment at 9S on sucrose gradients prepared in low ionic strength buffers. However, the receptor from the virgin mice is susceptible to cleavage,resulting in the appearance of 3–4S forms of the receptor. If, however, phosphate buffers or buffers containing sodium molybdate are used in the preparation of cytosol and its analysis, it preserves the integrity of the native 9S estrogen receptor.