Cytosol oestrogen receptor of lactating mammary gland. Effect of heparin on the aggregation of the receptor and interaction of the receptor with heparin-Sepharose

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Abstract
An estrogen receptor was present in low-salt cytosol of the mammary gland of lactating mice as a large aggregate; it was excluded from gel matrix when filtered on a Sephadex G-200 column and sediments at 7S [Svedberg unit] in sucrose gradients. After incubation of cytosol with heparin, the receptor was dissociated. On a Sephadex G-200 column, it was included in the gel matrix and eluted as a protein with MW 260,000 and a Stokes radius of 6.8 nm; it sedimented at 6S in sucrose gradients. Dissociation of the mammary-gland cytosol estrogen receptor seemed to be the result of interaction of the estrogen-receptor complex with heparin. This receptor interacted with heparin covalently bound to Sepharose, thereafter sedimenting at 6S. By using this interaction, the cytosol receptor was purified 200-fold compared with the homogenate, with a yield of 70%. The cytosol receptor that was not incubated or was incubated with heparin was much smaller during sucrose-gradient centrifugation than during gel filtration. This discrepancy can be explained by pressure-induced dissociation during high-speed centrifugation. This possibility was supported by the decrease in the sedimentation coefficient of the receptor with increased duration of centrifugation.