Characterization of an estrogen receptor in the turtle testis

Using DNA-cellulose affinity chromatography, an estrogen-binding component having the properties of a classical estrogen receptor was characterized from testicular cytosol of the freshwater turtle, Chrysemys picta. This putative cytoplasmic receptor exhibited high affinity (Kd = 7.0 X 10(-10) M), low capacity (1-4 fmol/mg protein), and steroid binding that was specific for estrogens. It was not present in plasma, muscle, kidney, or lung. A temperature-dependent conversion of turtle testicular estrogen receptor from 4 to 5 S occurred on DNA-cellulose columns, and resembled that in mammalian testis and other target tissues. After a single injection of estrogen at 3 hr, cytoplasmic receptors were depleted with a concomitant increase of nuclear receptors. Identification in turtle testis of an estrogen-binding macromolecule having the physicochemical properties of mammalian estrogen receptors is further evidence that receptors have been widely conserved in many tissue types through vertebrate phylogeny and supports the idea that the testis is an important target of estrogen action.