Abstract
Recent studies of the uterine estrogen receptor indicate it is a multi-subunit protein. Estradiol and temperature induce a conformational change in the 4 S estrogen-binding protein (EBP) or monomer (mol. wt. 7–8 × 10 4) as indicated by the high energy of activation (19–21 kcal mol −1) accompanying the formation of the 4S EBP dimer, 5S EBP (mol. wt. 13–14 × 10 4). The formation of the 5 S EBP suggests that new intramolecular bonding forces have been established, presumably hydrophobic interactions, which were not available in the inactive 4 S EBP monomer. Kinetic analysis of the 4 S to 5 S EBP transformation indicates a second-order reaction, the dimerization of the 4 S EBP with a second (similar or dissimilar) subunit. The 5 S EBP produced by the in vitro warming of the cytosol-[ 3H]-estradiol and the 5 S EBP extracted from isolated nuclei have similar molecular weights, sedimentation coefficients, molecular radii and rates of formation. These results suggest that an estradiol and temperature induced conformational change in the 4 S EBP leads to a macromolecular association process and receptor activation.
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