Estrogen-binding proteins in the oviduct of the turtle, Chrysemys picta: evidence for a receptor species.

Estradiol-binding proteins in the reproductive tract of the turtle, Chrysemys picta, were characterized. Cytosol was prepared from the oviducts of mature female turtles, and estradiol binding was measured using charcoal adsorption and glycerol density gradient centrifugation. A sex steroid-binding protein (SBP) similar to that found in turtle plasma was demonstrated in oviduct cytosol. The characteristics of this SBP-like binding were as follows: Ka = 10(8) M-1; capacity, 10(-12) mol/mg protein; and sedimentation coefficient, 6--7S in low salt gradients. The SBP-like protein binds testosterone and progesterone as well as 17 beta-estradiol but does not bind diethylstilbestrol. No receptor-like binding activity could be demonstrated using these techniques. Explant culture and DNA cellulose affinity chromatography were used to remove the SBP-like material before assay of [3H]estradiol binding. Using these techniques, a high affinity (Ka = 10(9) M-1), low capacity (n = 10(-14) mol/mg cytosol protein) estradiol receptor was demonstrated. The putative turtle receptor exhibits steroid specificity and sedimentation profiles (6S and 8S in low salt, 4S and 5S in high salt) comparable to those of estrogen receptors in mammalian species. These results suggest a certain degree of physiochemical similarity between putative estrogen receptors in mammalian and turtle reproductive tracts.