PURIFICATION OF THE CYTOPLASMIC ESTROGEN-RECEPTOR FROM MAMMARY-TUMORS 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 with 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 K(m) (dissociation constant) at 4°C for [3H]oestradiol-17β 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.