RESUMEN
The purification of estrogen- and progesterone-binding proteins of human uterus by employing affinity resins coupled with steroid-bovine serum albumin conjugates, led to the isolation of preparations with estrogen- and progesterone-binding sites having Kd values in the range of 0·96 to 1·20 × 10–9 M. These were different from the Kd values of 10–10 Μ and 10–8 Μ obtained for two types of binding sites present in the crude cytosolic and nuclear fractions. The purified proteins sedimented on sucrose gradient with S values in the range of 3·6–4·4. The cytosolic and nuclear estrogen- and progesterone-binding proteins, thus purified, showed differences in specificity of binding to the hormone. While the cytoplasmic proteins were more specific in their binding to estradiol or progesterone, the nuclear proteins bound Cortisol with equal or moderate affnity. These results demonstrate the presence of distinct physiological forms of estrogen- and progesterone-binding proteins in the cytoplasm and nucleus, thus pointing to the importance of both these compartments in hormone action. Keywords. Human.