A comparative study of electrophoretic mobilities of [³H]-estradiol and monohydroxytamoxifen binding components in the cytosols of human breast carcinomas and sera of healthy adult females

Cytosols from human breast carcinomas rich in estrogen receptors (ER) were examined for the presence of [³H]-estradiol (E₂) and [³H]-monohydroxytamoxifen (OH-TX) binding components. Polyacrylamide gel electrophoresis was used to examine the comparative anodal mobilities of ER-[³H]-E₂ and ER-[³H]-OH-TX complexes, and also to identify any cytosol or serum component that may exhibit preferential high affinity to OH-TX. We have demonstrated that [³H]-OH-TX binds ER with high affinity and the anodal mobility of ER-[³H]-OH-TX complexes is identical to that of ER-[³H]-E₂ complexes. We were unable to identify an antiestrogen-specific component in ER-positive or ER-negative cytosols or in sera of healthy adult females. A serum component exhibiting a higher affinity to [³H]-OH-TX and [³H]-DES than to [³H]-E₂ has been identified in all the female sera examined, but this binding is of high capacity and is unsaturable by a 1000-fold molar excess of unlabeled E₂ or antiestrogens. The electrophoretic mobility of this component is comparable to that of serum albumin.