Binding of the Sulfates of Estradiol-17β to Human Serum Albumin and Plasma

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Abstract
The binding of the 3 estradiol-17β sulfates in solutions of human serum albumin (HSA) and in plasma has been studied by the method of centrifugal ultrafiltration. HSA has one binding site for the 17-sulfate with association constants of about 105 to 106M−1 at either 4° or 37° and several sites with association constants of 103 to 104M−1. HSA has 3 groups of binding sites for estradiol-17β disulfate, one binding site with association constants of about 106M−1 at either 4 C or 37 C, about 2 binding sites with association constants of about 104M−1 and several sites with association constants of about 103M−1. The binding data of the 3-sulfate of estradiol-17β are best interpreted by the postulate of the existence of a tetramer in addition to the monomer of the sulfate in solution. With this postulate, HSA has one binding site with an association constant of about 5 · 105M−1 and seven binding sites with association constants of about 103M−1 at either 4 C or 37 C. More than 99% of the 17-sulfate or the disulfate of estradiol-17β is bound in plasma at 37°, with all of the binding accounted for by HSA. The estradiol-17β sulfates compete with one another for binding o t HSA. Strong displacement has also been found by androgen sulfates and, less, by estrogen glucosiduronates.

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