ATP-dependent enzyme activating hormone binding of estradiol receptor

Mouse uterus estradiol receptor undergoes a inactivation-reactivation process "in vitro". The specific estrogen binding activity inactivated by nuclei, apparently through a dephosphorylation process (1,2,3), is reactivated by an ATP-dependent process. The enzyme reactivating the receptor has been purified from calf uterus cytosol. It shows high affinity for the inactive receptor (K_m of ∼ 0.3 × 10^-9 mol of 17β-estradiol binding sites/l); it is simulated by MgCl₂ and CaCl₂. Present and previous results suggest that in cytoplasm of intact cells a phosphorylation process makes the receptor able to bind hormone and in nuclei dephosphorylation of receptor causes loss of hormone binding activity.