Evidence for the existence of an androgen binding protein in hydatidiform mole vesicles

Extracts of hydatidiform mole vesicles and the fluid contained in these vesicles were shown to contain a trophoblastic androgen binding protein. This protein was found to be distinct from serum testosterone-estradiol binding globulin (TEBG) by its isoelectric point, its affinity for dihydrotestosterone (DHT) and by Concanavalin A binding. The elution pH of this binding protein was shown to be 4.6, whereas that of TEBG was pH 5.2-5.3. The apparent dissociation constant (Kd app) for TEBG as determined by Scatchard analysis was 2.0 X 10(-9) M, whereas the Kd app for the trophoblastic binding protein after isoelectric focusing was 1.5 X 10(-10) M. A second binding protein found in both vesicular extracts and mole fluid was shown to have an isoelectric elution value (pH 5.2) similar to TEBG and an Kd app of 1.7 X 10(-9) M DHT, very close to the TEBG value. Apparent equilibration for both proteins with DHT was shown to occur in approximately 4H, and both proteins were shown to be high affinity, low capacity binders. The relative affinities of both proteins for other steroids was found to be similar except for methyltrienolone, which appeared to have a higher affinity for the trophoblastic binding protein.