CHARACTERIZATION OF THE PLASMA SEX STEROID-BINDING PROTEIN IN EEL (ANGUILLA-JAPONICA)

Sex steroid-binding protein was purified from the plasma of an eel, An guilla japonica. Testosterone and estradiol-binding activity existed a t the same fraction when eluted from gel Sepharose CL-2B, DEAE-Sephace l, hydroxylapatite and HPLC. The mass weight of the sex steroid-bindin g protein was 64,000 Da. At 50% displacement, in which the steroids di splaced tritiated testosterone or estradiol-17 beta bound to the bindi ng protein, the effect was as follows: estradiol-17 beta, androstenedi ol and testosterone were the most effective competitors, 11-ketotestos terone competed less well, and another 10 steroids were poor competito rs. The data suggest that the structure with specific C- and D-rings a nd hydroxyl groups on carbon 17 of the steroids is important for the s trong interaction of steroid and sex steroid-binding protein in the ee l.