The endometrial nuclear estradiol receptor of the pregnant cow has a molecular weight of 53000 in 6 M guanidine-HCl

Abstract

Cell nuclei isolated from the endometrium of the 3 months pregnant cow were dialysed against 6 M guanidine-HCl + 0.1 M 2-mercaptoethanol. The resulting material (after eliminating the bulk of DNA by centrifugation) was filtered on a Sepharose 6/b column equilibrated in the above denaturing solvent. The molecular weight of the denatured “nuclear” estradiol receptor, estimated by a method described previously (T. Erdos and J. Friés (1974) Biochem. Biophys. Res. Commun. 58, 932–939), was about 53 000. This value is similar to that of the cytoplasmic receptor (55 000) but dissimilar to that of the cytoplasmic receptor transformed by the action of the Receptor Transforming Factor (35 000) estimated under the same experimental conditions, suggesting that the latter form of the receptor is not the biological precursor of the “nuclear” receptor. However, according to indirect estimates, probably not more than 10% of the “nuclear” receptor has been renatured in these experiments. Therefore the alternative that the results obtained are not representative for the “nuclear” receptor, cannot be excluded.