Antiestrogen binding sites: General and comparative properties

Nonsteroidal antiestrogens, such as tamoxifen, bind estrogen receptors with relatively high affinity. They also bind with high affinity and distinctive specificity to another class of intracellular sites, often termed “antiestrogen binding sites” or “AEBS”. These sites do not bind estrogens and their function is unknown. In this article we compare and contrast the binding specificity, intracellular localization, concentration, tissue distribution and detergent solubilization characteristics of AEBS from a number of species. In general the sites are found in highest concentration in microsomal fractions from liver. AEBS from chicken liver can be solubilized with CHAPS detergent giving rise to a detergent-associated complex with an apparent molecular mass of about 265 kDa.