Effect of metal ions on the binding of 17beta-estradiol to human endometrial cytosol.

The influence of zinc and other metal ions on the binding of 3H-17beta-estradiol to human endometrial cytosol was studied. Zn2+ began to interfere with estrogen binding when its concentration in the cytosol exceeded 50 micronM. At a concentration of 5 mM, all of the specific binding of 17beta-estradiol, including more than 50% of the nonspecific binding of the hormone, was destroyed. Analysis of the binding data revealed that one possible site of action of the cations on the binding protein might be the sulfhydryl group(s) of the 17beta-estradiol binding site. The inhibition of 17beta-estradiol binding brought about by Zn2+ was partially abolished by dithiothreitol. Among the metal ions tested, Cu2+ was found to be the most potent inhibitor, followed by Cd2+, Zn2+, and Pb2+. At 1 mM, Mn2+, Ba2+, Ca2+, and Mg2+ had little effect, but at 5 mM, their inhibitory action became more appreciable. K+ and Na+ had no effect on 17beta-estradiol binding. The stimulatory effect of 5 mM Zn2+, Ca2+, Mg2+, and K+ on the binding of 3H-17beta-estradiol to a macromolecular fraction from bovine endometrium was not observed in human endometrial cytosol.