Androgen binding proteins in Cochliobolus lunatus

Testosterone and 4-androstene-3,17-dione (androstenedione) binding proteins were found in the cytosol of Cochliobolus lunatus, a filamentous fungus. The maximal androgen binding occurred by 120 min at 0 degrees C. Androgen binding proteins were degraded by protease treatment and at high temperature. The mean Kd determined for testosterone binding protein (TBP) by Scatchard analysis was 4.5 nM and the maximum capacity Bmax was 120 fmol/mg protein; for androstenedione binding protein (ABP) the Kd was 8 nM and Bmax was 390 fmol/mg protein. Steroid binding specificity for TBP, in order of decreasing affinity, was the following: androstenedione, progesterone, dihydrotestosterone, 17 beta-estradiol and estrone. The same order was found for ABP.