Analysis of Two Forms of the Molybdate- Stabilized Estrogen Receptor*

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Abstract
The calf uterine estrogen receptor prepared in 10-mM molybdate eluted as 2 components (peaks I and II) from DEAE-Sephadex columns with a linear KCl gradient. Unoccupied cytosol receptors also elute as 2 peaks (0.21 and 0.25 M KCl), as determined by postlabeling experiments with [3H]estradiol. Since molybdate-stabilized cytosol estrogen receptors incubated in the presence of 0.3 M KCl as well as estrgoen receptors in peak I and II did not demonstrate receptor binding to DNA-cellulose, than that both receptor forms are nonactivated. Also [3H]estradiol-receptor complexes from cytosol prepared in 10 mM molybdate sediment as 6.7S in 5-20% sucrose density gradients containing 0.3 M KCl, whereas receptor complexes from cytosol prepared without molybdate sediment as 4.5S. Both peaks I and II were eluted from DEAE-Sephadex columns prepared with either 10 mM molybdate or 10 mM tungstate, with both phosphatase inhibitors having effectively blocked salt activation of the receptor. However, receptor preparations in the presence of 10 mM arsenate were not eluted from DEAE-Sephadex, and arsenate was unable to inhibit receptor activation by KCl. Sucrose density gradient analysis of peaks I and II indicates that peak I sediments at .apprx. 4.8S, whereas peak II sediments at approximately 6.3S. If pooled fractions of the leading portion of peak I are rechromatographed on another DEAE-Sephadex column, both peaks I and II are recovered. Likewise, if pooled fractions of the descending portion of peak II are rechromatographed, both peaks I and II were measured. There may be an equilibrium between 2 forms of the molybdate-stabilized calf uterine estrogen receptor.

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