Filtration of calf uterine cytosol on ultrogel ACA 34 prevents aggregation of the estradiol receptor

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The Stokes radius of the estradiol receptor from calf uterus cytosol has been estimated to be 6.7 nm and 5.4 nm in low and high ionic strength medium, respectively [1,2] . However, the use of gel filtration (Sephadex G-200 or agarose) for the characterization of the ‘native’ estradiol receptor is questionable. In low salt medium, the receptor (8 S) is largely excluded from the gel, contrary to its behaviour in high salt medium (5 S-KCl) where it is not excluded. However in both cases, it is eluded in a broad peak, reflecting heterogeneous aggregation states of the receptor [3--S]. In presence of 0.1 M thiocyanate, it is possible to prevent the aggregation of the receptor, and its Stokes radius is 3.6 nm [6]. In the present paper it is reported that the filtration of the cytosol on ultrogel ACA 34, contrary to what is observed with the classically used gels, allowed the elution of the receptor as a symmetrical peak after the void volume of the column, in low as in high salt medium. The Stokes radius of the receptor was measured in low and high ionic strength buffers. A study of the filtration conditions for this type of gel was undertaken and led to a simple method of preventing aggregation of the estradiol receptor.