Abstract
The cytoplasmic dehydroepiandrosterone 3-sulfate (DHAS)-binding macromolecule in the cytosol fraction of human fetal membrane has been investigated. It was distinguished from serum DHAS-binding component on the basis of binding specificity and molecular weight. Scatchard analysis indicated a single class of binding sites (57 fmol/mg protein) with an apparent dissociation constant of 7.2×10-8M. The cytoplasmic DHAS-binding macromolecule was separated into two moieties by Sephacyl S-300 chromatography. One was eluted at void volume, and the other hand a molecular weight of about 1.7×105. These two moieties had the same specificity for DHAS, and had no affinity for dehydroepiandrosterone or 17β-estradiol. Progesterone, 5α-dihydrotestosterone and sulfated estrogens such as 17β-estradiol 3-sulfate, estriol 3-sulfate and estrone 3-sulfate showed much lower affinity for the DHAS-binding macromolecule. Themperature-dependent nuclear uptake of [3H]DHAS in a cell-free system required the presence of cytosol, suggesting that binding of DHAS to the cytoplasmic macromolecule is a prerequisite for the transfer of DHAS to the nucleus. These data demonstrate the presence in human fetal membrane of a tissue-specific DHAS-binding macromolecule which has properties similar to those of the DHAS-binding protein previously found in rabbit uterine cervix (A. Ito, K. Sakyo, H. Sano, S. Hirakawa and Y. Mori, Chem. Pharm. Bull., 34, 2118 (1986).
