Purification of the cytoplasmic oestrogen receptor from mammary tumours induced in rats with dimethylbenzanthracene.

The oestrogen receptor from mammary tumours induced in rats by dimethylbenz(a)-anthracene has been extensively purified by affinity chromatography and isoelectric focusing. The unpurified cytoplasmic 8 S oestrogen receptor had a molecular weight of 240,000, a Stokes radius of 5.4 nm and a frictional ratio of 1.32; the Km (dissociation constant) at 4 degrees C for [3H]oestradiol-17 beta was 0.184 nmol/l. At the end of affinity chromatography the molecular weight was still 240,000 but under the conditions of isoelectric focusing it was reduced to 110,000, with a Stokes radius of 4.0 nm, a frictional ratio of 1.26 and an isoelectric point of 6.4.