A specific progesterone-binding component of human breast cyst fluid.

The steroid hormone-binding properties of human breast cyst fluid were investigated and compared to those of female serum. Breast cyst fluid exhibited a high binding affinity for progesterone and pregnenolone, but very little affinity for cortisol, 17a-hydroxyprogesterone, and deoxycorticosterone. Serum exhibited a high binding affinity for progesterone, and also for cortisol, 17c+hydroxyprogesterone, and deoxycorticosterone; but only little affinity for pregnenolone. It thus appears that the progesterone-binding component (or components) of breast cyst fluid is unique, since its steroid-binding properties are distinctly different from those of the progesterone-binding component of human serum, i.e. corticosteroid-binding globulin. Breast cyst fluid, in contrast to female serum, exhibited a low binding affinity for 17/3-estradiol and testosterone. Column chromatography of breast cyst fluid on hydroxylapatite and DEAE-cellulose afforded considerable purification of the steroid-binding component (or components). Although the progesteroneand pregnenolone-binding component (or components) were eluted simultaneously from the chromatographic columns, identity is not presumed. According to a gel filtration study, the Stokes radius of the steroid-binding component (or components) appears to be about 38 A, corresponding to a molecular weight of about 72,000 for a globular protein. Of more general interest are the other proteins in breast cyst fluid which are present in high concentration, at least one-fourth of that of serum; the proteins of cyst fluid do not, however, resemble those of serum on polyacrylamide gel electrophoresis.