Interaction between rat alpha 1 fetoprotein and fluorescent derivatives of estrone in relation to the position and type of the fluorescent label.

A series of derivatives of estrone with fluorescent dyes (dansyl or coumarin) coupled at different positions on the steroid molecule, have been synthesized. These derivatives were tested for their quantum yields and their binding properties were determined with respect to rat alpha 1 fetoprotein. Derivatives at C-3 (estrone-3-hemisuccinate-dansyl-cadaverine and estrone-3-dansyl) compete with estrone for binding to the fetal protein; however derivates of estrone at C-6 (estrone-6-carboxymethyloxime-dansyl-cadaverine) and at C-17 (estrone-17-carboxymethyloxime-coumarine, estrone-17-carboxymethyloxime-dansyl-cadaverine and estrone-17-dansyl-hydrazine) compete poorly or not at all. The association constant of the radioactive derivative estrone-3-dansyl [3H] with rat alpha 1 fetoprotein was measured directly: the same number of high affinity binding sites (0.6) as that for estrone was found with an apparent association constant of 3.7 X 10(6) M-1. In addition to the high affinity binding sites, a low affinity class of binding sites was found which corresponds to the binding of the dansyl fraction of the fluorescent steroid derivative.