Properties of estradiol binding components in hamster uterine nuclei

Only one estrogen-binding component (Type I) was observed in salt (0.5 M KCl) extracts of proestrous hamster uterine nuclei. In addition to the classical estrogen receptor (Type I), a second binding component (Type II) was detected by [3H]estradiol exchange assay performed with hamster uterine nuclear suspensions. Although this Type II binder was not detected in salt extracts, a similar binding component was found in the nuclear debris remaining after salt extraction. The Type II binding component in the nuclear debris did not possess estrogen-binding specificity. Lack of specificity for estrogens, resistance to KCl extraction, and high capacity differentiated this Type II binder from the classical estrogen receptor. Preparation of nuclear fractions in buffer containing glycerol and monothioglycerol resulted in greater recovery of nuclear estrogen receptor (Type I) as compared to buffer lacking these constituents.